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Question: When the current is switched on through a wire, a compass needle kept nearby gets deflected from its north-south position. Explain. [2 MARKS]

 
Options:

: Reason: 2 Marks

When current is passed through a wire it starts behaving as a magnet. This happens due to the magnetic effect of electric current.
Hence, when a compass needle is placed near the given current carrying wire, it gets influenced by the magnetic effect of electric current and gets deflected from its North-South position.

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Question 1. In an electric bell, when the electromagnet pulls the iron strip, it also breaks the circuit. The current through the coil stops flowing. In this case, will the coil remain an electromagnet? How does an electric bell ring then? [3 MARKS]

: Working of electric bell: 3 Marks

The coil is no longer an electromagnet. It no longer attracts the iron strip.
The iron strip comes back to its original position and touches the contact screw again. This completes the circuit. The current flows in the coil and the hammer strikes the gong again. This process is repeated in quick succession.
The hammer strikes the gong every time the circuit is complete.
This is how an electric bell rings. The continuous breaking and completing of the circuit enable the gong to strike the hammer continuously.
Question 2. What are the various components of an electric bell? Explain the working of an electric bell.  [5 MARKS]

 

: Components: 2 Mark
Working: 3 Marks

An electric bell consists of a coil of wire. An electromagnet 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, current flows through the coil which becomes an electromagnet.
It, then,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.
However, when the electromagnet pulls the iron strip, it also breaks the circuit. The current through the coil stops flowing and it isno longer an electromagnet. It no longer attracts the iron strip.The iron strip comes back to its original position and touches the contact screw again.
This completes the circuit. The current flows in the coil and the hammer strikes the gong again.
This process is repeated in quick succession.The hammer strikes the gong every time the circuit is complete. This is how the bell rings.

Question 3. Explain the function of a switch in an electric circuit?  [2 MARKS]

: Explanation: 2 Marks

A switch is a device used to make or break an electric circuit.When the switch is in the ‘ON’ position, the circuit from the positive terminal of the battery to the negative terminal is complete. The circuit is then said to be closed and the current flows throughout the circuit instantly.

When the switch is in the ‘OFF’ position, the circuit is incomplete. It is said to be open. No current flows through any part of the circuit.
Question 4. Why are CFL bulbs preferred over filament bulbs? How do we know that an appliance is safe for use?  [3 MARKS]

 

: Advantages: 2 Marks
Safe mark: 1 Mark

An incandescent bulb is used for light but it also gives too much of heat. This is not desirable. This results in the wastage of electricity. This wastage can be reduced by using fluorescent tube lights in place of the bulbs.
Compact fluorescent lamps (CFLs) also reduce wastage and can be fixed in the ordinary bulb holders.
CFLs are more efficient than filament bulbs in terms of energy consumption. The ISI mark ensures that the appliance is safe for use, reliable and is made up of good quality.
Question 5. (a) What does MCB stand for? Explain the working of MCBs. Why are they preferred over fuses? 



(b) Name the principle on which electric fuse works?

[3 MARKS]

: Part (a) : 2 Marks
Part (b) : 1 Mark

(a) MCB stands forMiniature circuit breakers.

MCBs are basically a substitute for fuses.These are switches which automatically turn off when the current in a circuit exceeds the safe limit. We turn them on and the circuit is once again complete.
They are preferredover fuses because they are much more user-friendly, because if there is excess current in the circuit they automatically turn off, and the circuit is complete again if we turn it on. While in afuse, the fuse has to be replaced once excess current passes through it.

(b)Electric fuse works on the principle of the heating effect of current.
Question 6. The figure shows four cells fixed on a board. Draw lines to indicate how you will connect their terminals with wires to make a battery of four cells.  [1 MARK]



 

 

: Explanation: 1 Mark
Diagram: 1 Mark


The positive terminals of the cell will be connected to negative terminal of the cell and vice versa with the wire to make it a battery.

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