Chapter – Electricity
Class – 7
Subjective Questions
1. Draw the circuit symbol for the following: a. Cell b. Battery c. Bulb d. Switch (OFF) e. Switch (ON)
3. State three precautions that should be exercised while dealing with electricity.
• Never touch electrical appliances with wet hands • Do not use damaged or naked wires • Always switch off the main supply before repairing appliances
4. Why is the insulation coating removed from connecting wires before making circuits?
The insulation coating is removed so that the metal wire comes in direct contact with other components of the circuit, allowing electric current to flow.
5. Using a simple circuit, how will you identify conductors and insulators?
If the bulb glows when an object is placed in the circuit, the object is a conductor. If the bulb does not glow, the object is an insulator.
Exemplar Problems
1. How will the glow of bulbs in a series circuit change if the number of bulbs is decreased, keeping all other factors constant?
The bulbs will glow brighter because the total resistance of the circuit decreases and more current flows through the circuit.
2. Why does a fused incandescent bulb not light up?
In a fused bulb, the filament breaks and the circuit becomes incomplete. Hence, current cannot flow and the bulb does not glow.
Draw and Learn
Draw the internal structure of a dry cell and explain its working.
A dry cell consists of a zinc container (negative terminal), a carbon rod (positive terminal), ammonium chloride paste as electrolyte and manganese dioxide as depolariser. When the circuit is completed, chemical reactions inside the cell produce electric current which flows through the external circuit.
Look – Observe – Interpret
1. Identify the type of circuits shown in figures (a) and (b).
Figure (a): Series circuit Figure (b): Parallel circuit
2. In which circuit will the bulbs glow more brightly? Why?
Bulbs glow more brightly in a parallel circuit because each bulb receives the full voltage of the battery.
3. If bulb B is fused, will bulb A glow in figures (a) and (b)?
In a series circuit, bulb A will not glow. In a parallel circuit, bulb A will continue to glow.
4. Which circuit should be preferred as a domestic circuit? Give reasons.
Parallel circuit should be preferred because: • Appliances work independently • Same voltage is supplied to all appliances • Failure of one appliance does not affect others
