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Class 7 | Chapter 13: Electric Current and It's Effects.


A. Answer in Detail: 

1. How will you make an electromagnet in the laboratory?


Ans: An electromagnet can be made easily in the laboratory by following these steps:

  • First we have to take a soft iron nail.
  • Then we wind insulated copper wire tightly around the nail many times.
  • Connect the two free ends of the wire to a battery.
  • When the circuit is completed, electric current flows through the wire and the iron nail becomes magnetised.

Result:
The iron nail behaves like a magnet as long as current flows. When the current is switched off, it loses magnetism.

2. With the help of a diagram, show the working of an electric bell.

Answer:


Working of an Electric Bell:

  • When the switch is pressed, electric current flows through the coil.
  • The coil becomes an electromagnet and attracts the iron armature.
  • The hammer attached to the armature strikes the gong and produces sound.
  • This breaks the circuit, the electromagnet loses magnetism, and the armature returns to its original position.
  • The circuit is completed again and the process repeats rapidly.

Thus, the bell rings continuously.

3. What is electric resistance? How is it used in an electric bulb?

Ans: Electric resistance is the property of a conductor that opposes the flow of electric current.

Use of resistance in an electric bulb:

  • The filament of an electric bulb is made of tungsten, which has high resistance.
  • When current flows through it, the filament becomes very hot and glows, producing light.

4. What are conductors? How are they useful in an electric circuit?

Ans: Conductors are materials that allow electric current to pass through them easily.

Examples: Copper, aluminium, iron.

Usefulness in an electric circuit:

  • Conductors are used as connecting wires.
  • They help in the smooth flow of current between different components of a circuit.

B. Answer Briefly

1. What is meant by an open circuit? Why does electric current not pass in this case?

Answer: An open circuit is a circuit in which the path of current is broken or incomplete.

Electric current does not pass because there is no continuous path for the flow of current.

2. Why does a nichrome wire get heated in an electric circuit?

Ans: Nichrome wire has high resistance.
When current flows through it, electrical energy is converted into heat energy, so the wire gets heated.

3. What material is used to make the fuse wire? Can you use any metallic wire as a fuse wire? Give reasons.

 Ans: Fuse wire is made of a thin wire of low melting point, usually an alloy of tin and lead.
No, we cannot use any metallic wire as a fuse wire because:
  • Fuse wire must melt quickly when excess current flows.
  • Ordinary wires have high melting points and will not melt easily.

4. What are the causes of fire in electric circuits?

Ans: Fires in electric circuits may be caused due to:

  • Short circuit
  • Overloading
  • Loose connections
  • Use of damaged or poor-quality wires


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