D. Tick (ü) the odd-one out giving reason.
1. Silver, Graphite, Quartz, Brass, Gold
Ans. Quartz
2. Rubber, Metals, Alloys, Graphite, Wet clothes
Ans. Rubber
3. Battery of cells, Switch, Flashlight bulb, Thread
Ans. Thread
II. LOGIC-BASED QUESTIONS
Short and Long Answer
1. What is meant by a closed electrical circuit ?
Ans. A closed electrical circuit is a circuit in which the path for current is complete, so electric current flows from one terminal of the cell to the other through all components.
2. Why are the handles of tools like pliers used by electricians for repair work usually have plastic covers on them ?
Ans. The metal part of pliers conducts electricity, so handles are covered with plastic (an insulator) to protect electricians from electric shock while working on live wires.
3. Can electric wires be covered with aluminium foil instead of rubber or PVC ? Give reason.
Ans. No. Aluminium is a conductor, not an insulator, so it cannot prevent shocks or short circuits. Rubber and PVC are insulators, so they safely cover the conducting copper or aluminium wires.
4. Complete the following pattern using the following options :
gold ring silver coin glass rod copper wire
Aluminium foil : conductor : _________ : insulator
Ans. Aluminium foil : conductor :: glass rod : insulator
5. Riddhi is making a circuit using a wire, cell and an incandescent lamp. But she ran out of connecting wires. Which of the following options can she use to complete her circuit and why ?
rubber pipe glass bangle steel spoon thick thread
Ans. She should use a steel spoon, because it is made of metal and conducts electricity. Rubber pipe, glass bangle and thick thread are insulators and will not complete the circuit.
6. Why does the bulb not glow in the given circuit? What arrangement will make the bulb glow ?
Ans. The bulb does not glow because the circuit is open or the connections do not form a complete path from one terminal of the cell back to the other through the bulb. To make it glow, connect the wires so that they form a closed loop: one terminal of the cell to one terminal of the bulb, and the other terminal of the bulb back to the other terminal of the cell.
7. What is the role of electric switch in a circuit ? What kind of material is used for making the body/casing of electrical switches ?
Ans. A switch makes or breaks an electric circuit; when ON (closed), current flows; when OFF (open), current stops. The body/casing of switches is made of insulating materials such as plastic, bakelite or PVC to prevent electric shock.
8. Describe an experiment to find out whether the given material is a conductor or an insulator.
Ans. • Make a simple circuit: cell, bulb and connecting wires, but leave a small gap between two wire ends.
• Place the test material in the gap so it touches both wire ends.
• If the bulb glows, the material is a conductor; if the bulb does not glow, it is an insulator.
III. HIGHER ORDER THINKING SKILLS
1. Sometimes an incandescent lamp does not glow even when connected to a cell. What could be a possible reason ?
Ans. Incandescent lamp does not glow even when connected to a cell – possible reason. The bulb may be fused (filament broken), the cell may be weak/dead, or there may be a loose/incorrect connection in the circuit.
2. Is human body a conductor or nonconductor of electricity ?
Ans. The human body is a conductor of electricity, so electric current passing through it can cause serious injury or death.
3. An electrician while handling any electrical appliance/circuit wears rubber shoes and/or rubber gloves. Why ?
Ans. Rubber is an insulator, so rubber shoes and gloves prevent electric current from passing through their body to the ground, protecting them from electric shocks.
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