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CBSE Questions for Class 7 Physics Electric Current And Its Effects Quiz 5 - MCQExams.com
CBSE
Class 7 Physics
Electric Current And Its Effects
Quiz 5
The purpose of armature in an electric bell is
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to make and break the circuit
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to produce sound
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to produce magnetic field
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to provide spring action
Explanation
The purpose of armature in an electric bell
is 1. to make and break the circuit 2. to produce sound.
An electric bell uses an electromagnet.
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True
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False
Explanation
An electric bell
is a mechanical or
electronic bell
that functions by means of an
electromagnet
.When
an electric
current flows through the coils, the
electromagnet
creates a magnetic field which pulls the armature towards it, causing the hammer to strike the
bell
.
An electric bell has an electromagnet.
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True
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False
Explanation
An electric bell works with the help of an electromagnet. It is made up of a coil of wire wound on an iron piece, which acts as an electromagnet. On passing the current, the magnetic field is produced by the electromagnet. The hammer of the bell is attracted towards the electromagnet when the circuit is complete.
If the switch is connected to a bulb and the battery is kept in the on position what do you observe?
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The bulb will glow
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The bulb remains off
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Cannot say
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None of the above
Explanation
When the switch is turned ON the circuit completes and the bulb starts to glow. When the switch is turned OFF the bulb does not glow. So circuit has two states on which the bulb depends. So we cannot determine by just connecting the switch in the circuit.
What does ISI mark imply?
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The appliance is safe
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The electricity would be overused
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Extra heat is produced in the appliance
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Wastage of energy is minimum
Explanation
The ISI mark ensures that the appliance is safe and wastage
of energy is minimum, hence options $$A&D$$ are correct.
What is incorrect about CFLs?
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They gives out a lot of heat
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They reduce wastage
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They can be fixed in the ordinary bulb holders
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None of these
Explanation
Compact fluorescent lamps (CFLs) give out less heat then ordinary bulbs, reduce wastage and can be fixed in the ordinary bulb holders hence option $$A$$ is incorrect.
Which among the following pair of elements are suitable in the construction of electric bell?
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X, Y
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Y, Z
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X, Z
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X, Y, Z
Explanation
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The electric bell consists of a _______ wound on an _______.
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iron piece, wire
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wire, another wire
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iron piece, another iron piece
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wire, iron piece
Explanation
An electric bell has a coil of wire wound around a piece of iron which acts like an electromagnet. An iron strip with a hammer 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, current flows through the coil and becomes an electromagnet.
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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First $$B$$ then $$C$$ and then $$A$$
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First $$A$$ then $$B$$ and then $$C$$
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First $$A$$ then $$B$$ and $$C$$
together
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All the bulbs will glow together
Explanation
When the switch is moved to the on position, the circuit is closed. All the bulbs will glow together.
What is kept close to the electromagnet in the electric bell?
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Iron piece
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Coil wire
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Iron strip with a hammer
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Gong
Explanation
An iron strip (armature) with a hammer at one end is kept close to the electromagnet in an electric bell, thus option $$C$$ is correct
Which of the following acts an electromagnet in an electric bell?
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The iron piece
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The coil
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The armature
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The gong
Explanation
The electric bell consists of a coil of wire wound on an iron piece. When the current flow through the coil, it acts as a magnet. Magnetic property in the coil develop due to current flow so this magnet is known as electromagnet.
thus option $$B$$ is correct.
The diagram shows the circuit of an door bell. What happens when the bell button is switched on then switched off?
Switch on
Swithc off
(A)
$$1$$ ting is heard
Silence
(B)
$$1$$ ting is heard
$$1$$ ting is heard
(C)
Continuous
Silence
(D)
Silence
Continuous ringing
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A
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B
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C
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D
Explanation
In the given bell circuit, when we press the bell button (switched on), current will flow through the circuit and the solenoid will become magnetised. It will produce magnetic field that will attract the soft iron which will hit the gong 1. So a ting will be heard.
After switching off, the solenoid will become demagnetised and will not produce magnetic field. The soft iron won't be attracted. The hammer will come back to its mean position due to the pull of the spring metal strip. The other (right) face of the hammer will hit the gong 2. So another ting is heard.
What is the missing label at $$\star$$ ?
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Contact Screw.
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Pointer
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Key
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Brush
Explanation
The element marked $$\star$$ is called the contact screw.
Contact screw completes the circuit in an electric bell. When the iron strip is in contact with the screw , the current flows through the coil and it becomes an electromagnet. The hammer at one end of iron strip strikes the gong and bell is rung.
Symbol of switch in 'ON' position is -
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0%
0%
0%
Explanation
Third option is the symbol of 'on' switch.
Answer-(C)
Identify the circuit (Figure 12.3) in which the electrical components have been properly connected
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(I)
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(II)
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(III)
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(IV)
Explanation
Hint:
Check the connections of the Voltmeter and Ammeter.
Step 1: Checking if the Voltmeter is connected in parallel and Ammeter is connected in series.
In circuits $$(i)$$ and $$(iii)$$, Voltmeter is connected in series. In circuit $$(iii)$$ the ammeter is connected in parallel. In circuits $$(i)$$ and $$(iii)$$, connections are not proper.
In circuits $$(ii)$$ and $$(iv)$$, the Voltmeter and Ammeter are connected in parallel and series respectively.
Step 2: Checking if the terminals are connected properly.
In circuit $$(iv)$$, the positive terminal of the ammeter is connected with the negative terminal of the cell. Hence it is not proper.
Whereas in circuit $$(ii)$$, all the terminals are properly connected. Therefore option $$(B)$$ is the correct option.
Would any of the bulbs glow when the switch is in the 'off' position?
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Bulb $$A$$
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Bulb $$B$$
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Bulb $$C$$
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None of the above
Explanation
When the switch is in the 'off'. position, no bulb will glow as the circuit is incomplete and no current flows through the circuit.Also these bulbs are in series which means that if current through one lamp is zero , current through every lamp will be zero and no bulb will lig
ht up.
Correct option is (D).
Which of the following is directly responsible for the production of sound in an electric bell?
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The coil
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The iron piece
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The gong
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The switch
Explanation
The hammer at the end of the strip strikes the gong of the bell to produce a sound, thus option $$C$$ is correct.
The electric bell has an electromagnet in it.
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True
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False
Explanation
An electric bell consists of a coil of wire on an iron piece. The coil acts as an electromagnet.
Choose whether true or false:-
Electric fuses are wires that melt quickly.
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True
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False
Explanation
Wires made from some special materials melt quickly and break when large electric currents are passed through them and fuses are made from them, hence the given statement is correct.
What happens when the electromagnet pulls the iron strip in an electric bell?
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It completes the circuit
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It breaks the circuit
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The current stops flowing
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Both $$B$$ & $$C$$
Explanation
In an electric bell,when the electromagnet pulls the iron strip, it breaks the circuit because that iron strip was part of the circuit.Since current only flows in closed circuits,the current through the coil stops flowing, thus option $$D$$ is correct
Choose whether true or false:-
CFLs need special place to be put up.
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True
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False
Explanation
Compact fluorescent lamps (CFLs) reduce wastage and can be fixed in the ordinary bulb holders, hence the given statement is false.
Which of the following is the reason for overflow of current in circuits?
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The direct touching of wires
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Connection of many devices to a single socket
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Using a fuse
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Both $$A$$ & $$B$$
Explanation
Reasons for excessive currents in
electrical circuits are the direct
touching of wires and the
connection of many devices to a single
socket, hence option $$D$$ is correct.
Fuse prevents fires in circuits.
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True
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False
Explanation
Fuse is a safety device that prevents damages to electrical circuits and possible fires, hence the given statement is true.
A "circuit breaker" or "fuse" is a safety device designed to prevent accidental overloading of electrical circuits. They are set at a specific amperage. When that amperage is exceeded, it trips and shuts off the flow of electricity, stopping the circuit from continued overheating.
There is a _______ limit on the current which can safely flow through a ________
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Minimum, building
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Maximum, building
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Minimum, circuit
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Maximum, circuit
When is the circuit complete of an electric bell?
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When the iron strip touches the contact screw
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When the iron strip is no longer attracted by the coil
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When the hammer doesn't strike the gong
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When the bell no longer rings
Explanation
When the
iron strip comes back to its original
position and touches the contact screw
again, it completes the circuit, thus option $$A$$ is correct.
In which of the following cases is the Heating Effect of Electric Current demonstrated in household appliances?
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Electric toaster
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Geyser
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Television
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Refrigerator
Explanation
$$\textbf{Concept applied:}$$ Applications of Heating Effect of Electric Current
$$\textbf{Correct Options: A, B}$$
$$\textbf{Explanation for Correct Options:}$$ Electric toaster and geyser are required to produce heat for different household purposes. They have a heating element which generates heat when electricity is passed through them. So they demonstrate the "
heating effect of electric current
".
$$\textbf{Explanation for Incorrect Options:}$$The working principle of Television and Refrigerator are not based on Heating Effect of Electric Current.
Which of the following is not a function of a fuse?
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Blowing off and breaking the circuit
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Preventing damages to electrical circuits
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Preventing possible fires
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Glowing
Explanation
A fuse is a safety device which prevents damages to electrical circuits and possible fires by
blowing off and breaking the circuit,when currect exceeds a maximum value. Fuse does not glow .Hence option $$D$$ is correct.
Choose whether true or false:-
The image shown above is a correct depiction of heating effect of electric current.
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True
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False
Explanation
An electric heater works on the principle of heating effect of electric current, hence the given depiction is true.
Take an electric cell, a bulb, a switch and connecting wires. Make an electric circuit as shown in this figure above. This activity has to be done using only one cell. Keep the switch in the OFF position and touch the bulb. What do you feel?
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The bulb is slightly warm to touch
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The bulb is extremely cold to touch
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The bulb is very hot
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The bulb is at normal temperature
Explanation
$$\textbf{Concept applied:}$$
Heating Effect of Electric Current
$$\textbf{Correct option: D}$$
$$\textbf{Explanation:}$$
$$\bullet$$ Since the switch is kept in an 'OFF' position, the circuit does not form a closed path. We know current only flows in a closed circuit. So NO current will flow in the circuit.
$$\bullet$$ According to the heating effect of electric current, the CURRENT flowing through an element produces HEAT.
$$\bullet$$ Since no current is flowing in the bulb, NO heat will be generated, and the bulb will remain at its Normal Temperature.
Make a circuit as shown in the figure above. Take about $$10\ cm$$ long piece of nichrome wire and tie it between the nails. (You can get nichrome wire from an electric repair shop or you can use a piece of a discarded coil of an electric heater.) Touch the wire. Now switch on the current in the circuit by moving the switch to the ‘ON’ position. After a few seconds touch the wire. What difference do you observe?
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No difference
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The wire becomes very hot
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The wire becomes cold
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The wire is slightly warm to touch
Explanation
When an electric current flows through the nichrome wire, the wire gets heated. It is
the heating effect of current.
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