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CBSE Questions for Class 7 Physics Electric Current And Its Effects Quiz 2 - MCQExams.com
CBSE
Class 7 Physics
Electric Current And Its Effects
Quiz 2
Symbol denotes
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Resistance and voltmeter respectively
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Plug key and switch respectively
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Load and Key respectively
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Tapping key and switch respectively
Explanation
The symbol shown in the figure represents a tapping key and a switch respectively.
Tapping key: a light flexible metallic strip provided with contacts so that when it is momentarily pressed an electric circuit is made or broken and when it is released the opposite effect is automatically produced.
Switch: a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another.
Which of the following is a plug key?
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All of the above
Explanation
The following symbols are shown in the circuit diagram:
(a) Plug key
(b) Switch key
(c) Tapping key
A straight line represents which electric component
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Load
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Resistor
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Conducting wire
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Cell
Explanation
Electrical symbol of cell, resistor, conducting wire and cell are shown in the figure.
Thus a straight line in an electrical circuit represents a conducting wire.
Given figure is a symbol of
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Bulb
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Battery
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Switch
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Fixed resistance
Explanation
Electrical symbols of bulb, battery, switch and fixed resistance are shown in the figure.
Thus symbol shown in the question represents a switch. A switch is used to make or break a connection in the electrical circuit.
Option C
Which of the following is an advantage of using electrical symbol?
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It makes the representation of electrical component easy.
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It makes the circuit drawing easier.
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It helps in solving the circuits.
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All of the above.
Explanation
The uses of electrical symbols are listed below:
1. It eases the representation of an electrical component.
2. It makes the circuit drawing easier and more compact.
3. It gives important insights into the circuits and increases the speed of solving electrical circuits.
Figure shows a
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plug key
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switch key
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tapping key
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none of the above
Explanation
$$\textbf{Explanation:}$$ A switch is an electric component that opens or closes a circuit. We know that electricity can only pass across a circuit if it is closed. The switch is usually wired in series with the load it is attempting to control.
$$\textbf{Option B is correct}$$
Which of the following is a symbol of tapping key.
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All
Explanation
Figure in option A represents a plug key, option B is the symbol of switch whereas figure in option C represents a tapping key.
What does this symbol mean in electric circuits?
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Rheostat
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Battery
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capacitor
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Inductance
Explanation
Rheostat is a variable resistor, which is used to control the flow of electric current by manually increasing or decreasing the resistance. The arrow sign indicates the variability.
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Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
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Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
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Assertion is correct but Reason is incorrect
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Both Assertion and Reason are incorrect
Explanation
If AC source is used in electric bell, As it changes the polarity, it continuous by magnetizes and demagnetizes .
Though attraction of strip does not depend on polarity but the strength of attraction surely depend on amplitude which must be high.
Which power supply can be used in electric bell
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$$AC$$
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$$DC$$
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Can't be predicted
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Both A and B
Explanation
Electric bell works on the mechanism of electromagnets and for this, any type of power either AC or DC can be used.
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.
Which of the following symbol is used for a diode in circuits?
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Explanation
A diode has an anode on one side and a cathode on the other side and is represented by this diagram.
Answer-(C)
Symbol of power source in electric circuit is-
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Explanation
The symbol of a power source has two lines - one shorter and the other one is longer. The shorter line represents the negative end and the longer line represents the positive end of the source.
Which of the following symbols used for current generating source?
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None of these
Explanation
A is symbol of voltage source
B is a symbol used for current generating source.
And, C is a symbol of transformer.
Therefore, B is correct option.
Which of the following is not a component of electric bell?
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Gong
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Ferromagnetic strip
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Low magnetic field permanent magnet to attract ferromagnetic strip
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None of the above
Explanation
Electric bell works on the mechanism of electromagnets i.e, temporary magnets, and no permanent magnet is used.
Temporary magnet allows the ferromagnetic strip to return back to its initial state as switch is released.
Which of the following is a characteristic of a buzzer?
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It has different mechanism from electric bell.
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It has higher frequency of collision of gong and hammer
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It uses only AC power supply
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None of the above
Explanation
In a buzzer, the simplest sort of doorbell, an electromagnet is used to operate a self-interrupting circuit. You can see how this system works in the diagram below. Click and hold the doorbell button to see how the buzzer works. ... This breaks the doorbell circuit, which shuts off the electromagnet.characteristic of a buzzer It has higher frequency of collision of gong and hammer
Which pair is not correct for the instruments used in the laboratory and their uses from the following?
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Voltmeter - To measure the electric potential differene
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Ammeter - To measure the electric current
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Galvanometer - To detect the presence of current
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Resistor - To supply the electric energy to circuit
Explanation
A resistor is an instrument which provides a resistance to the flow of current. Electric energy to the circuit is provided by a battery.
What is the minimum number of cells require to make a battery?
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5 cells
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2 cells
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1 cell
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6 cells
Explanation
A combination of two or
more cells is called a battery.
The minimum number of cells require to make a battery is $$2$$.
Which of the following is/are energy efficient products?
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Tube lights
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Bulbs
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LEDs
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CFLs
Explanation
The electricity used over the lifetime of a single incandescent bulb costs 5 to 10 times the original purchase price of the bulb itself. Light Emitting Diode (LED) and Compact Fluorescent Lights (CFL) bulbs have revolutionized energy-efficient lighting.Because both CFL and LEDS use very less power as compared to bulbs. CFLs are simply miniature versions of full-sized fluorescents.And LED is a semiconductor device.
Which of the following is the function of MCB in household circuit?
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This switch automatically turns off when current exceeds safe limit
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This switch automatically turns on when current exceeds safe limit
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Saves the electrical appliances from getting damaged due to excess current
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Saves from short-circuiting
Explanation
An MCB functions by breaking the flow of electric current through the circuit once a fault is detected. In simple terms, MCB is a switch which automatically turns off when the current flowing through it passes the maximum allowable limit.
A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by excess current from an overload or short circuit. Its basic function is to interrupt current flow after a fault is detected.
What is the full form of MCB?
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Micro Circuit Breakers
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Miniature Circuit Breakers
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Miniature Circuit Builders
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Mega Circuit Blockers
Explanation
An MCB or miniature circuit breaker is an electromagnetic device that is used as a safety device in the circuit.
Which of the following will produce maximum wastage of electricity ?
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CFL
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Electric bulb
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LED lights
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All are power savers
Explanation
The electric bulb works by heating up a small wire called the filament. Electric current heats the filament so much that it glows. In fact, $$90\%$$ of the electricity used by a electric bulb is converted to heat and this conversion produces maximum wastage of electrical energy.
Choose the correct option
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MCB is much more sensitive to over current than fuse
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Fuse is much more sensitive to over current than MCB
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Handling MCB is more electrically safe than fuse
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Handling fuse is more electrically safe than MCB
Explanation
Fuse is an electrical device that self-destructs and stops the current flow in a circuit whenever the current exceeds the predefined value. MCBs are resettable circuit protection device that, on the occurrence of faults, stops the current flow in a circuit.
Nowadays MCB in low voltage electrical network is commonly used instead of fuse. The fuse may not sense the overcurrent but the miniature circuit breaker does it in a more reliable way. MCB is much more sensitive to over current than fuse. Handling a MCB is electrically safer than a fuse.
Choose the correct combination of cells to form a battery
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All of the above
Explanation
A cell has two terminals - positive and negative. When two or more cells are connected end to end, i.e. positive end is connected to the negative end, then it forms a battery. Therefore all the above combinations of cells are indicating the formation of a battery.
What is/are the advantage of MCB over fuses?
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Its wire melts unlike fuses wire
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It automatically turn off to save from excess electricity
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It takes less time to break the circuit as compare to fuse while overloading
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None of these
Explanation
MCB has several advantages over fuse:
MCB is more sensitive to current than the fuse. It detects any abnormality in the current flow and automatically switches off the electrical circuit.
In the case of MCB, the fault zone of the electrical circuit can be easily identified. Faulty circuit trips to the off position. On the other hand in case of the fuse, the complete fuse wire needs to be checked by opening fuse grip for confirming the fault zone.
With MCB it is very simple to resume to the supply. You just need to push the knob of MCB back to on position. But in case of the fuse, the entire fuse wire needs to be replaced.
MCB provides a better interface with the help of knob than a fuse. In case of the fuse, the compete for handle needs to be taken care out.
Handling MCB is electrically safer than handling a fuse.
MCB is reusable and hence has less maintenance and replacement cost. Whereas a fuse needs to be replaced whenever it goes faulty.
Electromagnets are used in which of the following?
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Speaker
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Motor
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Generator
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All of the above
Explanation
Electromagnets are formed by passing an electric current through a wire coiled around the substance with iron core.
Electromagnets are used to speaker, motor and generator.
A fuse is connected to the live wire.
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True
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False
Explanation
A fuse is a circuit element made of high resistance material that melts when there is overloading in the circuit. It is always connected to the live wire to break the circuit preventing the connected devices from damage.
A student sets up a circuit containing a battery of two cells and three lamps, as shown.
What is the circuit diagram for this arrangement?
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Explanation
The correct option is $$(A)$$.
From the figure, it is clear that , two cells are connected in series,
two bulbs are connected in parallel and
one bulb is connected in series with parallel combination of two bulbs.
Electromagnets are made up of:
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$$steel$$
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$$copper$$
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$$soft$$ $$iron$$
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$$aluminum$$
Explanation
Electromagnets are formed by the wounding of conducting wires like coil over the soft iron core.
Hence All option can be correct.
State true or false.
MCB is a safety device which cuts off the electricity supply automatically without turning off a switch.
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True
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False
Explanation
MCB stands for miniature circuit breaker. A MCB is an electrical device that is automatically controlled to protect an electrical circuit from damage caused by excess current from overload or short circuiting. MCB prevents damage by
automatically breaking the circuit without turning off any switch.
Which of the following is the correct method of setting a circuit?
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None of the above
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