a. Give reasons for the following:
i. Tungsten used almost exclusively for filament of electric lamp.
ii. Copper and aluminium wires are usually employed for electricity transmission.
b. Describe an activity with the help of circuit diagram to show that potential difference across each resistor connected in parallel is same.
a. i. Electric lamp works on the principle of the heating effect of electric current, so when current passes through the filament of bulb, a large amount of heat is produced making the filament of the bulb to emit light. So the temperature rises to a maximum value, and the material of filament should be such that it can withstand maximum temperature without melting. So tungsten is used as it has a high melting point of 3380oC, hence it is used exclusively for the filament of electric lamps.
ii. Copper and aluminum are metals so they have free electrons present in them which makes them good conductors of electricity. Their resistivity is also very low so they are employed for the transmission of electricity.
b. 1. Three resistors R1, R2, R3 are connected in parallel as shown in the diagram below. A battery, key, ammeter, voltmeter is connected.
2. Key is plugged in and ammeter, voltmeter readings are noted down.
3. Then key is taken out along with ammeter and voltmeter.
4. Ammeter is connected in series and voltmeter in parallel with resistor R1. Readings are noted down.
5. Above step is repeated for resistor R2 and R3.
6. Readings are noted for three resistors it would be found that ammeter readings for three resistors are different but voltmeter readings are same.
This proves that potential difference is same across three resistors connected in parallel since voltmeter measures the potential difference across resistors.