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1. Choose the correct option.

a. Choose the standard symbol of a bulb for a circuit diagram.
i.
Answer: (i)

b. What is the SI unit of potential difference?
i. ampere
ii. joule
iii. newton
iv. volt

• Answer: (iv) volt

c. Which of the following appliances are used to convert electrical energy to heat energy?
i. Geyser
ii. Television
iii. Electrical bell
iv. Speaker

• Answer: (i) Geyser

d. Why does the fuse wire break when an excess of electricity passes through a fuse?
i. It has a low resistance.
ii. It has a low melting point.
iii. It is a good conductor of heat.
iv. It is a good conductor of electricity.

• Answer: (ii) It has a low melting point.

2. Assertion-Reasoning Questions.

(i)

• Assertion (A): LED bulbs are more efficient than filament-based bulbs.
• Reason (R): Filament bulbs work on the heating effect of an electric current.
• Answer: (b) Both Assertion (A) and Reason (R) are true, and Reason (R) is not the correct explanation of the Assertion (A).

(ii)

• Assertion (A): An electromagnet is a temporary magnet.
• Reason (R): An electromagnet loses its magnetism in the absence of current.
• Answer: (a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).

3. Answer the following questions in one sentence.

a. What is the use of an ammeter?

Answer: An ammeter is used to measure the electric current flowing through a circuit.

b. Four cells of 2 V each are connected to form a battery. What is the voltage of this battery?

Answer: The voltage of the battery will be 8 V.

c. How is an electrical fuse useful?

• Answer: An electrical fuse is useful because it protects electrical circuits and appliances from damage caused by excessive current flow.

d. Explain the term ‘magnetic effect of electric current’.

• Answer: The magnetic effect of electric current is the phenomenon where an electric current flowing through a conductor produces a magnetic field around it.

4. Answer the following questions in 2-3 sentences.

a. Name the electrical component that is used to protect electrical components like LED in a simple circuit from an excess of current. How does this component protect the LED?

• Answer: A resistor is used to protect components like an LED. It protects the LED by limiting the amount of current that can flow through the circuit, thereby preventing the LED from burning out due to high current.

b. How can we make a magnet using a connecting wire and a battery?

• Answer: We can make a magnet by taking a long connecting wire and wrapping it around an iron nail to form a coil. When we connect the ends of the wire to a battery, the nail becomes an electromagnet.

c. State two uses of an electromagnet.

Answer: Two uses of an electromagnet are:

In electric bells to produce sound.

In cranes to lift and move heavy iron and steel scrap.

d. What is a short circuit? What is the possible effect of a short circuit?

• Answer: A short circuit occurs when the live (positive) and neutral (negative) wires in a circuit come into direct contact, offering very low resistance. The possible effect is a sudden, very high current flow which can cause overheating, sparks, and electrical fires.

5. Answer the following in 3-4 sentences.

a. A student constructs an electric circuit. She brings a magnetic compass close to the connecting wire of the electric circuit.
i. What would she observe when the current passes through the circuit?

• Answer: When the current passes through the circuit, she would observe the needle of the magnetic compass deflect from its north-south position.

ii. What would she observe when the current stops flowing through the circuit?

• Answer: When the current stops flowing, the compass needle would return to its original north-south position.

iii. What can she conclude from this activity?

• Answer: From this activity, she can conclude that an electric current produces a magnetic field around its conductor.

b. State the precautions that must be taken while drawing an electric circuit.

• Precautions when drawing an electric circuit include using a sharp pencil to draw neat and clean lines, ensuring all connections are shown correctly, using standard symbols for components, and ensuring the circuit diagram is properly labeled.

c. What is an electromagnet? What are the factors that affect the strength of an electromagnet?

• Answer: An electromagnet is a temporary magnet that acts like a magnet only when an electric current flows through it. The factors that affect its strength are: the number of turns in the coil, the strength of the current passed through it, and the nature of the core material (using an iron core makes it stronger).

d. A water heater contains an element. What will be the effect produced by the heater, if:
i. The length of the element becomes double

• Answer: If the length doubles, the resistance of the element increases, which would reduce the current and produce less heat.

ii. the thickness of the element becomes half

• Answer: If the thickness is halved, the resistance increases, leading to reduced current and less heat production.

iii. the flow of current increases through the element

• Answer: If the flow of current increases, the heating effect will be greater, and the heater will produce more heat.