1. What is an open circuit?
Ans. A circuit in which the electrical contact at any point is broken is called an open circuit.
2. Why do tube lights (or fluorescent tubes) not generate heat?
Ans. A tube light or fluorescent tube does not generate heat because it does not contain a current-carrying filament.
3. What is an electric fuse? Where is it placed in the circuit?
Ans. An electric fuse is a safety device that prevents damage to electrical appliances and possible fire due to excessive current.
A fuse is placed in the live wire of the circuit.
4. On which effect of current is an electric bell based?
Ans. An electric bell is based on the magnetic effect of electric current.
Ans. Electromagnets are used in hospitals for removing iron splinters from wounds, in cranes for lifting heavy iron loads, and for separating magnetic substances from non-magnetic substances.
1. The bulb in the circuit shown alongside does not glow. Where is the fault in the circuit? Correct the fault and redraw the circuit diagram.
Ans. The cells are connected incorrectly. They should be placed one after the other, connecting the negative terminal of one cell to the positive terminal of the next.
The corrected connection is shown on the right (in the circuit diagram).
2. What is meant by the heating effect of current? Explain how a bulb glows.
Ans. The heating effect of current is the generation of heat in a resistor (or conductor) when an electric current passes through it.
Inside the glass shell of an electric bulb, there is a filament made of a very thin, high-resistance tungsten wire. When current flows through this filament, it gets heated up. Soon, it becomes white hot and starts emitting light — this is how the bulb glows.
3. What is the role of a fuse in an electrical circuit? Why is the fuse wire made of an alloy having a low melting point?
Ans. A fuse is a safety device that protects electrical appliances from damage due to excessive current.
The fuse wire is made of an alloy with a low melting point. When a large current passes through the circuit, the fuse wire gets heated up and melts, breaking the circuit. This stops the flow of current and prevents damage to the electrical appliances.
4. What is meant by the magnetic effect of current? Name three appliances based on this effect.
Ans. When an electric current passes through a wire, a magnetic field is produced around it. This phenomenon is called the magnetic effect of current.
Appliances based on this effect:
- Electric motor
- Electric bell
- Dynamo
5. What will you prefer — soft iron or steel — to make an electromagnet? Give reason.
Ans. Soft iron is preferred for making an electromagnet because it loses all its magnetism as soon as the current in the coil is switched off.
In contrast, steel does not lose its magnetism easily and becomes a permanent magnet.
1. Why cannot copper wire be used as a fuse wire?
Ans. A fuse wire is a thin wire made of a material that has a low melting point. It melts and breaks the circuit if the current exceeds the safety limit.
A copper wire cannot be used as a fuse wire because it has a high melting point. It would not melt easily even when a high electric current passes through it, which could lead to damage of electrical appliances.
2. A copper wire coil is suspended freely. When no current is passed through it, it comes to rest in any direction. Which direction will it point if current is passed through it?
Ans. When an electric current is passed through a copper wire coil, a magnetic field is produced around it, and the coil behaves like a magnet.
Since a freely suspended magnet always rests in the north–south direction, the coil will also come to rest in the north–south direction as long as the current flows through it.
3. You must have seen birds sitting on an overhead electric cable comfortably. Once in a while, a monkey (or any other small animal) swings between two parallel wires, gets electrocuted, and dies. Explain why.
Ans. When birds sit on an overhead electric cable, they sit on only one wire at a time. This does not complete the circuit, so no current flows through their bodies.
However, when a monkey or any other animal touches two parallel wires simultaneously, it completes the circuit, allowing current to flow from one wire to the other through its body. This results in a severe electric shock, often causing death.
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