7th Grade > Physics
ELECTRIC CURRENT AND ITS EFFECTS MCQs
Total Questions : 113
| Page 11 of 12 pages
Answer: Option A. ->
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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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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.
Answer: Option A. ->
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Naming: 1 Mark
Function: 1 Mark
Fuses are used as safety devices.
Fuses ensure that excessive current does not flow in the electric circuit. If excessive current flows in the electric circuit it may cause damage to the electric appliances.
There is a maximum limit on the current which can safely flow through a circuit. If by accident the current exceeds this safe limit, the wires may become overheated and may cause fire.
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Naming: 1 Mark
Function: 1 Mark
Fuses are used as safety devices.
Fuses ensure that excessive current does not flow in the electric circuit. If excessive current flows in the electric circuit it may cause damage to the electric appliances.
There is a maximum limit on the current which can safely flow through a circuit. If by accident the current exceeds this safe limit, the wires may become overheated and may cause fire.
Answer: Option A. ->
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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.
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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.
Answer: Option A. ->
:
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Each point: 1.5 Mark
1. When electric current flows through a wire, the wire gets heated. It is the heating effect of current or when current flows through a metal wire it gets heated up, this is called the heating effect of current. E.g. a glowing electric bulb becomes warm. This effect has many applications like Electric Heater, Light Bulb etc.
2. When an electric current flows through a wire, it produces magnetic effect around it. A current-carrying coil of an insulated wire wrapped around a piece of iron is an electromagnet. Magnetic effect of electric current has many applications like and is used in many objects like, electric bell, motor, fan etc
Answer: Option A. ->
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Part (a): 2 Marks
Part (b): 1 Marks
(a)
1. When an electric current is passed through the conductor, electrons collide with nearby electrons more frequently, which produce heating effect.
3. The increase in kinetic energy of atoms give rises to heat energy, which gives heating effect when current passes through the conductor.
(b) Toaster and electric geyser
Answer: Option A. ->
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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.
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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.
Answer: Option A. ->
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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.
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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.
Answer: Option A. ->
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Explanation: 1.5 Marks
Diagram: 1.5 Marks
In the fig., one end of the bulb is connected to the battery while the other end is connected with a safety pin which is a conductor. However, the other end battery is not connected with the safety pin which was required for the current to flow. Thus, the switch is in off position or circuit is not complete.
So the bulb will not glow.
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Explanation: 1.5 Marks
Diagram: 1.5 Marks
In the fig., one end of the bulb is connected to the battery while the other end is connected with a safety pin which is a conductor. However, the other end battery is not connected with the safety pin which was required for the current to flow. Thus, the switch is in off position or circuit is not complete.
So the bulb will not glow.
Answer: Option A. ->
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Part (a) : 2 Marks
Part (b) : 1 Mark
(a) MCB stands for Miniature 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 preferred over 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 a fuse, 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.
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Part (a) : 2 Marks
Part (b) : 1 Mark
(a) MCB stands for Miniature 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 preferred over 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 a fuse, 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.
Answer: Option A. ->
:
Factors: 0.5 Mark each
Working Principle: 1 Mark
The factors on which the amount of heat produced in a wire depends are:
1) its material
2) length of the wire
3) the thickness of the wire
4) the amount of current passing through the wire
The working of an electric bulb is based on the principle of the heating effect of electric current.
:
Factors: 0.5 Mark each
Working Principle: 1 Mark
The factors on which the amount of heat produced in a wire depends are:
1) its material
2) length of the wire
3) the thickness of the wire
4) the amount of current passing through the wire
The working of an electric bulb is based on the principle of the heating effect of electric current.
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