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Science [3 Marks Question]

T2 CH2 Electricity · Tamil Nadu Board STD 7 (Tamil - English Medium). 3 questions.

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[3 Marks Question]

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Question 13 Marks
Differentiate parallel and serial circuits.
Answer
1. Parallel circuits:
  1. It is connected by branches.
  2. Voltage remains the same across each component of the circuit
  3. Each bulb is fully powered.
  4. All bulbs stay lit if one goes out.
2. Serial circuits:
  1. It consist of single loop connection.
  2. Current remains same in all parts of the circuit.
  3. All the bulbs share power.
  4. All bulbs go out if one goes out.
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Question 23 Marks
Explain the heating effect of electric current.
Answer
  1. When an electric current passes through a wire, the electrical energy is converted to heat.
  2. In heating appliances, the heating element is made up of materials with high melting point. An example of such a material is nichrome (an alloy of nickel, iron and chromium).
  3. The heating effect of electric current has many practical applications.
  4. The electric bulb, geyser, iron box, immersible water heater are based on this effect.
  5. These appliances have heating coils of high resistance.
  6. Generation of heat due to electric current is known as the heating effect of electricity.
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Question 33 Marks
Explain the construction and working of an Telephone.
Answer
In telephones, a changing magnetic effect causes a thin sheet of metal (diaphragm) to vibrate. The diaphragm is made up a metal that can be attracted to magnets.
  1. The diaphragm is attached to spring that is fixed to the earpiece.
  2. When a current flows through the wires, the soft – iron bar becomes an electromagnet.
  3. The diaphragm becomes attracted to the electromagnet.
  4. As the person on the other end of the line speaks, his voice cause the current in the circuit to change. This causes the diaphragm in the earpiece to vibrate, producing sound.
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