Electric Current And Its Effects - Class 7 Physics - Extra Questions

In an electric bell, a flat ................. spring brings the armature back to its original position.

In an electric bell, a flat steel spring brings the armature back to its original position.
Working of an electric bell:
When the push button is pressed the electric circuit is completed and the armature is attracted towards the electromagnet as a result, the small spring gets detached from the screw due to which the electric circuit is broken and the electromagnet is demagnetized. Hence, the attraction disappears and the armature is brought back by the spring to its original position. Contact of the spring with the screw is now remade, which completes the electric circuit. The action is repeated over and over again consequently. The armature vibrates and the hammer attached to it strikes the gong and the bell rings and sound is produced.

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Why are the contact points of an electric bell made from silver-cadmium alloy?

Contact spring is a flat steel spring, slightly bent and fixed to the armature with the help of screws. The other end of the spring is attached to contact point A, made of silver-cadmium alloy. This alloy does not get oxidised easily due to sparkling.

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Name a common device that uses electromagnets.

Electromagnets are commonly used in electric bells.
An electric bell is a mechanical or electronic bell that functions by means of an electromagnet. When an electric current is applied, it produces a repetitive buzzing, clanging, or ringing sound.


_____________ is used in making electromagnets.

Electromagnets are temporary magnets that are due to the magnetic effect of electric current thus electric current is used.


The given image is a symbol of ______.
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The given symbol is the symbol of a resistor having some resistance.Resistance  is measured in ohm $$(\Omega)$$.


Choose the correct answer from the four alternatives given in the brackets:
The symbol of ammeter is ...............
($$V,A,G,I$$)

The symbol of ammeter is $$A$$. An ammeter (from Ampere Meter) is a measuring instrument used to measure the current in a circuit. Electric currents are measured in amperes ($$A$$), hence the name. Instruments used to measure smaller currents, in the milliampere or microampere range, are designated as milliammeters or microammeters.


Using the "conduction tester" on an object it was found that the bulb begins to glow. Is that object a conductor or an insulator? Explain.

Yes, if the object is good conductor of electricity then current will pas through conduction tester and the bulb will glow. Hence the object will be a conductor of electricity.


Write the full form of $$ M.C.B. $$

The full form of $$ M.C.B. $$ is : Miniature Circuit Breaker.

These are switches which automatically turn off when current in a circuit exceeds the safe limit. You turn them on and the circuit is once again complete.


Name the device used these days in place of electric fuses in electrical circuits.

The name of device is Miniature Circuit Breaker (MCB).


In the circuit shown in the figure.
I)Would any of the bulb glow when the switch is in the 'OFF' position?
II) What will be the order in which the bulbs A, B and C will glow when the switch is moved to the 'ON' position?

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$$I)$$ No, none of the bulbs will glow when the switch is the off position as the circuit won't be completed when the switch will be in the off state.

$$II)$$ All the bulbs will glow at once because all the bulbs are connected with the same battery and they are being controlled by the same switch.


A group of two or more cells is called a ..........

A group of two or more cells is called a battery.


Give the symbol of an electric fuse used in circuit diagrams.

The symbol of an electric fuse is shown in figure.
A fuse is an electrical safety device that operates to provide overcurrent protection of an electrical circuit. Its essential component is a metal wire or strip that melts when too much current flows through it, thereby stopping or interrupting the current.

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Unscramble the following word:
HTRCO

TORCH


Unscramble the following word:
SFEU

FUSE


What do the above symbol represent in the electric circuit ?
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Hence, given symbol in the question represents cell in electric circuit.
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With which wire is the fuse wire connected :  live or neutral

Live wire.
The fuse wire is always connected to the live wire of the electric circuit because if the fuse is somehow put in the neutral wire in the circuit, then due to excessive flow of electric current when the fuse burns, current will stop flowing in the circuit, but the appliance will still remain connected to the high potential point of the power supply through the live wire.


Read the extract given below and answer the question that follows:

The trees inside are moving out into the forest,
the forest that was empty all these days
where no bird could sit
no insect hide
no sun bury its feet in shadow
the forest that was empty all these nights
will be full of trees by morning.

The figure of speech used in these lines is _________ .
(i) Simile 
(ii) Alliteration
(iii) Personification 
(iv) Metonymy

When the push switch is depressed, the circuit is closed. Current passes through the electromagnet winding and the core becomes magnetized. The magnetized core attracts the iron armature which makes the striker hits the gong. However, the movement of the armature opens the make and break switch which switches the electromagnet off. The iron armature springs back to its original position, closing the make and break switch and start the cycle again. 
Soft iron core is used to make electromagnets as it gains and losses magnetism quickly depending on existence of magnetic fields. The armature is also made of soft iron which can induce magnetism rapidly. No matter what direction is the current flow, the bell rings continuously as long as the push switch is closed because any pole induces the armature.
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Explain the construction and working of electric bell with figure.

The electric bell works on the principle of the electromagnet. Its construction is shown in the above figure.
Construction: It is made of an electromagnet, bell(metallic cup), soft iron strip(which works as a hammer) and contact screw. The bell is a cup-shaped device made of metal. A soft iron strip works as a small hammer.
Working: When current is passed through the circuit, the electromagnet acts like a magnet and attracts the iron strip. The iron strip(hammer), being elastic, strikes the bell. Simultaneously, its contact with the screw is broken, the circuit breaks and the current stops flowing through the electromagnet. As such, the iron strip returns to its original position, and again the current passes through the electromagnet.
This phenomenon happens many times in a second, and as the hammer strikes the bell, the sound is heard. The bell rings till the circuit has been switched off. The electric bell is used in alarms and bells is schools, offices, homes and industries.

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State four most common electrical appliances based on heating effect of electric current. Why do we use finely heated platinum wire in surgery?

Appliances based on heating effect of electric current are:
1) Electric heater
2) Electric iron
3) Microwave oven
4) Induction cooker
Finely heated platinum wire is used in surgery rather than knife because melting point of platinum is $$1768\ ^\circ C$$ is very high so it does not get melted easily  when heated for cutting the tissues while doing surgery.



Given below are the symbols of a few electronic components. Select the component in which you can see a dielectric.
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Capacitor, in which there is a dielectric used to increase the capacitance.
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$$Match \ the \ following.$$

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In the diagram shown, all the four electrical components are correctly matched.
a) Plug key or switch is a device for making and breaking the connection in an electric circuit.
b) A wire joint is a joint by which two wires are united.
c) Electric bulb is an electric device with a wire filament heated to a high temperature, by passing an electric current through it, until it glows with visible light.
d) An electrical cell is a device that is used to generate electricity, or one that is used to make chemical reactions possible by applying electricity.

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What happens on connecting too many appliances at a time to a single socket?

Appliances are connected in parallel connection which leads to overall reduction in resistance in the circuit and more current flows through socket. Too many appliances in same socket means too much load connected parallely across same node. This will further  increase the current .  If the socket has no fuse, wiring of socket can burn as a result of this. 


In an household electrical circuit:
a) Where is the MCB ( Miniature Circuit Breaker ) connected?
b) What is the function of ELCB ( Earth Leakage Circuit Breaker )?

a) Instead of fuse, a miniature circuit breaker (MCB) is usually connected in series in electrical household circuits. It is connected in series at the beginning of each phase in the circuit. 
b) ELCB directly detects current leaking to the Earth from the circuit and cuts off the power.


Schematic of a rheostat is shown in the figure. Connect a battery to it so that the rheostat acts as a potential divider.
Specify which are the inputs and outputs terminals
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The output terminals are
(A,C) or (B,C) 

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What is an electromagnet? Describe the construction and working of an electromagnet with the help of a labelled diagram.

An electromagnet is a temporary magnet that works on the magnetic effect of current. It consists of a long coil of insulated copper wire wrapped around a soft iron core that is magnetised only when electric current us passed through the coil. 
To make an electromagnet, we take a rod $$NS$$ of soft iron and wind a coil of $$C$$ of insulated copper wire around it. When the two ends of the copper coil are connected to a battery, an electromagnet is formed.
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Explain the importance of using a fuse in a household electric circuit

A fuse is one of most important protection devices, which is avoiding the damages happen due to over load or short circuit.


Find the odd one out :
Voltmeter, Ammeter, Thermometer, Galvanometer.

Except for Thermometer all the other three appliances [Galvanometer, Voltmeter, Ammeter] are related to current electricity and normally used in electric circuit for the measurements of the parameters related to electricity where as the Thermometer is used for temperature measurement. 


Write daily life uses of heating effect of electric current.

Toaster$$,$$ geyser$$,$$ bulb and other electric applainces are daily use of heating effect of electric current$$.$$ 



An electric iron is rated at 230 V, 750 W. Calculate the maximum current:
Which of the following fuse rating would be suitable for this electric iron?
$$1\ A, 3\ A, 5\ A, 13\ A$$

$$V=230V, P=750W$$
Let max current be $$I$$
We have $$P=VI$$
$$750=230\times I$$
$$I=3.26\ A$$
$$5\ A$$ fuse rating will be suitable for this electric iron as the maximum current for this iron is $$3.26\ A$$.


Explain why, an electromagnet is called a temporary magnet.

An electromagnet is called a temporary magnet because it produces magnetic field so long as current flows in its coil.


Name two human body organs where magnetism produced is significant.

Brain and heart are the parts of the body where sufficient magnetism is produced.


Write the function of a fuse.


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Why are compact fluorescent lamps (CFLs) preferred over electric bulbs?

The electrical bulb uses more electric power and also wastes electrical energy in the form of heat. Whereas compact fluorescent lamps do not waste electrical energy in the form of heat and they also consume less energy.


Unscramble the following word:
TBTAYER

BATTERY


What do the following circuit symbols represents?

1774060_fcde8b396cdf46b99588cd8615183553.png

This symbol represents the electrical device known as Rheostat.
This electrical device is used to control  current by varying the resistance.


What device could be used in place of the fuses?

MCB (Miniature circuit breaker) are used in the circuits instead of fuse.


Why are fuse fitted in the fuse box of a domestic electricity supply?

Fuse is fitted in the fuse box of a domestic electricity supply to protect the whole wiring of the house when excessive current flows in the circuit.
The fuse breaks the circuit if a fault in an appliance causes too much current to flow. This protects the wiring and the appliance if something goes wrong. The fuse contains a piece of wire that melts easily. If the current going through the fuse is too great, the wire heats up until it melts and breaks the circuit.


Unscramble the following word:
HICWTS

SWITCH


Can we use the same fuse in a geyser and a television set? Explain.

A geyser is used to heat water.
For this reason, geyser needs a high rate of electricity.
Television is used to put pixels on the screen.
For this reason, television needs a low rate of electricity as compared to the geyser. 
So, according to the required rate of electricity we have to use different fuses in a geyser and television set.


Name two devices in which electricity is converted into heat.

The devices in which electricity is converted into heat Electric heater and electric iron.


Name two electric devices for each where
(i) heating effect of current is used and
(ii) magnetic effect of current is used.

The electric devices are
i) Heating effect of current is used: Room heater and geyser.
ii) Magnetic effect of current is used: Cranes and electric bell.


How does the magnetic effect of electric current help in the working of an electric bell? Explain with the help of a diagram.

The circuit of electric circuit is given below:
When we switch ON the circuit, electric current flows through the coil. According to the magnetic effect of current, the coil gets magnetized. This magnetized coil attracts nearby soft iron armature. Also because of this, the hammer strikes the gong (bell) to generate a sound. So, the bell starts buzzing. 
When we switch OFF the circuit, the magnetization of the coil and flow of current will stop. So, the bell stops buzzing.
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What is battery?

A battery is a device that stores chemical energy and converts it to electrical energy. It is used in applications where more electricity is needed like torch, toys, UPS, Car etc.

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Which fuse wire is thick : $$5A$$ or $$15A$$

$$R\ \alpha\ \dfrac{Length}{Area}$$ 
More the area, lesser is the resistance and more is the current flowing.
Hence , $$15A$$ is thicker wire .


Draw a neat and labelled diagram of an electric bell and describe its working.

$$\text{Working}$$
  • When a push button fitted in a battery is pressed, the current flows through the contact points via an electromagnet.
  • The U shaped electromagnet is magnetized and it attracts the armature towards it.
  • The hammer fitted with strip gives a strike on the gong producing sound.
  • The moment this happens, contact of the attached spring with screw is broken, i.e. the circuit is broken.
  • As a result, current stops flowing and the electromagnet is demagnetized.
  • Due to this action of the spring, armature comes to its previous position, i.e. comes in contact with the screw and the circuit is again completed.
  • Each approach of the armature or strip causes the hammer to strike the gong.
  • Thus, the same process is repeated many times and the bell goes on ringing.

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How is $$ M.C.B. $$ superior to the fuse wire?

$$ M.C.B. $$ automatically falls down and switch off the circuit in very short time, when excessive flow of electric current in a circuit.It is raised up after the fault is rectified.M.C.B doesn't need to be replaced everytime when high current passes through it but fuse needs to be replaced because it melts and breaks


Give reasons for the following.
Electromagnets are temporary magnets.

An electromagnet is a temporary magnet because it behaves like a magnet only till the current is passed through it. When the current is stopped, it stops behaving like a magnet.


Why is soft iron used as the core of the electromagnet in an electric bell? 

An electric bell consists of one or more electromagnets, made of a coil of insulated wire around an iron bar, which attract an iron strip armature with a clapper.
The soft iron bar acquires the magnetic properties only when an electric current flows through the coil and loses the magnetic properties as the current is switched off. That's why soft iron is used as the core of the electromagnet in an electric bell.Because it serves the purpose of a temporary magnet that can be turned off or on accordingly.


Write symbols and state function of the following component in an electric circuit:
Cell.

An electric cell is a device, which converts chemical energy into electrical energy. It has two terminals, positive and negative. When the two terminals are connected to an electrical device, electric current flows through it.
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What is the function of a key (or switch) in an electric circuit ?

The function of a key or a switch is to put on or off current in a circuit. It decides whether the circuit is complete or not.


Write symbols and state function of the following component in an electric circuit:
Voltmeter.

Voltmeter: Electrical instrument which is parallelly connected in the circuit. 
Function: Measures the potential difference between two points in a circuit.
Symbol: its symbol has added above.

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How is the working of an electric bell affected? If alternating current is used instead of direct current? 

If an A.C. source is used in place of the battery, the core of electromagnet will get magnetized, but the polarity at its ends will change. Since attraction of armature does not depend on the polarity of the electromagnet. so the bell will still ring on pressing the switch. 


Name the material used for making the armature of an electric bell. Give a reason for your answer.

The material used for making the armature of an electric bell is soft iron which can induce magnetism rapidly.


Describe with the aid of a diagram some form of a fuse which is used in the electric lighting circuit of a house.Give two reasons why a fuse must not be replaced by an ordinary copper wire.

The above figure shows the most common fuse arrangement in which the fuse wire is stretched between the two metallic terminals $$T_1$$ and $$T_2$$ in a porcelain holder.This holder fits into a porcelain socket having two metallic terminals to each of which the live wire of the circuit is connected.
A fuse must not be replaced with a copper wire because copper  has very low resistivity and high melting point. So it will not melt quickly because it will not produce much heat as compared to fuse wire.
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Write symbols and state function of the following component in an electric circuit:
Rheostat.

Components: Rheostat
Function: it controls the amount of current in a circuit by varying the net resistance of the whole circuit.
Symbol: Given in figure.

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Name the material of core in (a) electric bell. (b) electromagnet (c) d.c motor. (d) an a.c. generator and (e) transformer. 

The material used in the core of all the mentioned devices is the soft iron. As, it shows magnetism when current flows in the surrounding coil.


How is a fuse put in an electric circuit ? State the purpose of using a fuse in a circuit.

The fuse wire is stretched between the two metallic terminals.$$T_1$$  and $$T_2$$ in a porcelain holder (since porcelain is an insulator of electricity).This folder fits into a porcelain socket having two metallic terminals to which the live wires of the circuit are connected.The figure below is showing the fuse arrangement.
A fuse is connected with each electrical appliance to safeguard it form the flow of excessive current through it.


The incomplete diagram of an electric bell is given in Fig 10.21 Complete the diagram and label its different parts. 
1805437_331db93a93694d84bd822b026e1fb650.png

The complete diagram of the electric bell with all the labelled parts is as  shown.
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A coil of insulated copper wire is wound around a piece of soft iron and current is passed in the coil from a battery. What name is given to the device so obtained? Give one use of the device mentioned by you.

The device so obtained can be named an electromagnet.
One application of electromagnet is as follows:
Electromagnets are used in electrical devices such as telegraphs, electric bells, microphones, loudspeakers, etc.


What do the above symbol represent in the electric circuit ?
1831919_2f9f7e95e73a4067a194d2b1bc2a0839.png

The above symbol represent a resistor having some resistance in the electric circuit.


Why is soft iron used as the core of the electromagnet in an electric bell?

Soft iron can obtain magnetic properties when an electric current flows through the solenoid and has a tendency to lose magnetic properties when it is devoid of any electric current. This is the reason why soft iron is used as the core of the electromagnet in an electric bell.


What is an electromagnet ? Write the name of four appliances in which it is used ?

An electromagnet is a coil of insulated wire wound around a piece of magnetic substance, such as soft iron, which acts as a magnet only as long as the current is flowing in the wire. The magnetic material around which the coil is wound is called the core. The core increases the magnetic effect of the solenoid several times. They are used in electric motors, which find wide application in fans, washing machines, air conditioners, refrigerators, etc.


Why do we use symbols in an electrical circuit?

We use some standard symbols to represent different components of a circuit. Using symbols in a circuit makes it:
  • Easy to understand 
  • Quick to draw
  • Clean and clear in appearance.
  • Easier to trace the fault and repair it


What do the above symbol represent in the electric circuit ?
1831916_679fe20c649142a1899cce6696a63dfc.png

Plug-key
The plug key is used as a switch when pressed it to allow or interrupt the flow of current.

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What do the above symbol represent in the electric circuit ?
1831914_8a4e98c0b6954970b19566489aa3c8c2.png

Voltmeter.


Write any three applications of electromagnet.

Application of Electromagnet:
1. To separate things from scrape.
2. Accidentally pieces of magnet fall in eyes are removed from eyes by an electric magnet.
3. Electric magnet crane is used to lift heavy iron goods.


What do the above symbol represent in the electric circuit ?
1831921_9a58ded90b56492592c145569f98dd4d.png

Given symbol represent Variable resistance or Rheostat in the circuit.


Give two advantages of heating effect of electric current.

1)The heating effect of current is used in heating appliances such as electric iron, room heaters and water heaters. 
2) An electric fuse is an important application of the heating effect of current. The working principle of the fuse is based on the heating effect of current.


Name a device that helps to maintain a potential difference across a conductor.

$$\textbf{Explanation}$$

$$\bullet$$Potential difference is the difference of electrical potential between two points which is defined as the amount of work energy is required to move an electric charge from one point to another.

$$\bullet$$An electric cell or battery helps to maintain a potential difference across a conductor.

$$\bullet$$The cells only provide the energy required to work on the charge in order to transport it from the negative to the 

positive terminal. 

$$\bullet$$The cell can sustain an electric potential difference across the two ends of the external circuit by giving energy to the 

charge.




How does the room heater work?

The room heater or any heat appliances contain a coil of wire. This coil of wire is called an element which has resistance. When these appliances are switched 'on' after connecting to the electric circuit, then according to Joule's law of heating , the heat generated on passing of current through resistance makes the  element red hot and give out heat.


Where should we place the key or switch in the electric circuits?

The key or Switch can be placed anywhere in the electric circuit.


Write a short note on electric bell.

The electric bell works on the principle of electromagnet. Its construction is shown in the figure below.
It is made up of an electromagnet, a bell (metallic cup), a soft iron strip (which works as a hammer) and a contact screw. When current is passed through the circuit, the electromagnet acts like a magnet and attracts the iron strip. The iron strip (hammer) being elastic, strikes the bell. Simultaneously, its contact with the screw is broken and the circuit breaks and current stops flowing through the electromagnet. As such the iron strip comes back to its original position and again the current passes through the electromagnet. This phenomenon happens many times in a second and as the hammer strikes the bell, the sound is heard. The bell rings until the circuit is switched off.
Electric bell is used in school, at offices, home, alarms etc.
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When should we say that the circuit is closed?

A electrical circuit is said to be closed when current is started to flow after switch on.


How an electric bell works?

It consists of a coil of wire wound on an iron piece. The coil acts as an electromagnet. An iron strip with a hammer at one end is kept close to the electromagnet. There is a contact screw near the iron strip. When the iron strip is in contact with the screw, the current flows through the coil which becomes an electromagnet. Then it pulls the iron strip. In the process the hammer at the end of the strip strikes the gong of the bell to produce a sound.
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Observe the structure of a loudspeaker. 
Where is the voice coil situated?
1848211_1dbf2f91471e424cbd41a57a57a7f154.png

From the above picture,
The voice coil is situated In the magnetic filed.


What do the above symbol represent in the electric circuit ?
1831926_e6bdf28f01254fc695f58004052d21d2.png

The above symbol represent in the electric bulb.

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What is the symbol of a rheostat?


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Is the direction of current in a battery always from the negative terminal to the positive terminal? Explain.

No. When a battery serves as a source and supplies current to a circuit, the direction of the current is from the negative terminal of the battery to the positive one. However, when a source having a larger voltage than the battery is used to charge the battery, the direction of the current is from the positive terminal to the negative one.


If a sound is produced in front of a movable diaphragm, what will happen to the diaphragm?

If a sound is produced in front of a movable diaphragm, it vibrates corresponding to the sound signals.


A few heating appliances are shown in the above figure. Examine any one of them and answer the following question.
Name the part in which electrical energy changes into heat energy.
1850757_f378ce3bccbe44df8f89358a8660edf8.png

Heating coil changes the electrical energy into heat energy. An electric current passing through a resistor present in heating coil will convert that electrical energy into heat energy. It is working on the principle of joule's heating.


Instead of permanent magnets, electromagnets are used as field magnets in power generators. Find out reasons from the following and write them down. 
a. The strength of permanent magnets goes on decreasing.
b. The strength of electromagnets goes on decreasing.
c. Electromagnets can retain the required magnetic strength.

Electromagnet is a soft metal core made into a magnet by the passage of electric current through a coil surrounding it.
Instead of permanent magnets, electromagnets are used as field magnets in power generators because :
$$a.$$ The strength of permanent magnets goes on decreasing.
$$c.$$ Electromagnets can retain the required magnetic strength.
Statement $$b$$ is wrong because strength of electromagnet does not decrease , it depends on current flowing in coil.It's strength can be increased and decreased depending on current.


A transformer working on a $$240 \,V$$ AC supplies a voltage of $$8 \,V$$ to an electric bell in the circuit. The number of turns in the primary coil is $$4800.$$ Calculate the number of turns in the secondary coil.

$$V_{p} = 240\,V$$
$$V_{s} = 8\,V$$
$$N_{p} = 4800$$
$$\dfrac{V_s}{V_p} = \dfrac{N_s}{N_p}$$
$$N_{s} = \dfrac{V_s \times N_p}{V_p} = \dfrac{8 \times 4800}{240} = 160$$


An electric heater calibrated $$1.5\,kW, 230\,V$$ is connected to a household branch circuit having $$5$$ A fuse wire and is, made to work. What will happen?

Given,
The power rating of the electric heater, $$P=1.5\ kW=1500\ W$$
Voltage, $$V=230\ V$$
Safe current rating of fuse wire, $$I_{safe}=5\ A$$

We know,
$$P=VI$$

$$\implies I = \dfrac PV$$

$$\implies I = \dfrac {1500}{230}$$

$$I=6.52\ A$$

$$I\gt I_{fuse}$$
$$\therefore the fuse wire will burn$$


What are the differences between ordinary fuse and MCB ?

Ordinary fuse works making use of heating effect of electricity while MCB works making use of heating and magnetic effects of electricity. The current in the circuit may increase due to reasons such as short circuit, overload, excess flow of current or any problems in the insulation.
As the higher temperature produced in the circuit due to these reasons makes the fuse wire to melt and the flow of current stops. Thus the circuit and the appliances are protected. MCB automatically breaks the circuit whenever there is an excess flow of current due to short circuit or overloading. After rectifying the circuit we can switch on the MCB and make the circuit as it was.


If a sound is produced in front of a movable diaphragm, what will be the result?

If a sound is produced in front of a movable diaphragm then it creates an electric signal corresponding to the sound.


If a sound is produced in front of a movable diaphragm, What happens to the voice coil then ?

If a sound is produced in front of a movable diaphragm then voice coil will vibrates. 


Why is a fuse wire made of a tin-lead alloy and not copper?

A fuse wire is made of tin alloy because it has low melting point, so that it may melt easily, whereas a copper wire cannot be used as a fuse wire because it has a high melting point due to which it will not melt easily when a short circuit takes place.


State difference between the wire used in the element of an electric heater and in a fuse wire.

The wire used in the element of electric heater has a high resistivity and have a high melting point, i.e. even at a high temperature element do not burn while fuse wire have a low melting point and high resistivity.


What is an electromagnet ? List any two uses.

An electromagnet is a soft iron piece converted into a magnet when a current is passed in the wound coil around the iron piece.
Uses of Electromagnet-
1. The electric bells are based on principle of electromagnet.
2. The electromagnets are also used in motors and generators.

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What is a fuse wire? What is the advantage and disadvantage of using a thick fuse wire?

A fuse is a very important device used for protecting electric circuits. It is a wire made out of a metal like tin or tin alloy having a very low melting point. 
When a high current flows through a circuit, the fuse wire gets heated or melts due to short-circuiting or overloading. Hence the circuit is broken and the current stops flowing. This saves all the appliances of the circuit.


Draw an appropriate schematic diagram showing common domestic circuits and discuss the importance of fuse.


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Use circuit symbols to construct schematic diagrams for the following circuit:-
A single cell, light bulb and switch are placed together in a circuit such that the switch can be opened and closed to turn the light bulb on

The correct diagram is given here.
When switch is closed circuit gets complete and bulb glows and when  switch is in off position circuit is incomplete and bulb does not glow because for current to flow closed circuit is necessary.

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Class 7 Physics Extra Questions