Q. Several electric bulbs designed to be used on a 220 V electric supply line, are rated 10 W. How many lamps can be connected in parallel with each other across the two wires of 220 V line if the maximum allowable current is 5 A?

Q. Two lamps, one rated 100 W at 220 V, and the other 60 W at 220 V, are connected in parallel to electric mains supply. What current is drawn from the line if the supply voltage is 220 V?

Q. A piece of wire of resistance $R$ is cut into five equal parts. These parts are then connected in parallel. If the equivalent resistance of this combination is $R^{\prime }$, then the ratio $\frac{R}{R^{\prime }}$ is -

1. $\frac{1}{25}$
2. $\frac{1}{5}$
3. $5$
4. $25$

Q. A copper wire has diameter 0.5mm and resistivity of $1.6\times {10}^{-8}\Omega m$. What will be the length of this wire to make its resistance $10\Omega$? How much does the resistance change if the diameter is doubled?

Q.

Explain the following.

(a) Why is the tungsten used almost exclusively for filament of electric lamps?

(b) Why are the conductors of electric heating devices, such as bread-toasters and electric irons, made of an alloy rather than a pure metal?

(c) Why is the series arrangement not used for domestic circuits?

(d) How does the resistance of a wire vary with its area of cross section?

(e) Why are copper and aluminium wires usually employed for electricity transmission?

Q. A battery of 9 V is connected in series with resistors of $0.2\Omega ,0.3\Omega ,0.4\Omega ,0.5\Omega$ and $12\Omega$ respectively. How much current will flow through the $12\Omega$ resistor?

Q.

A hot plate of an electric oven connected to a 220 V line has two resistance coils A and B, each of $24\Omega$ resistance, which may be used separately in series or in parallel. What are the currents in three cases?

Q. Two conducting wires of the same material and of equal lengths and equal diameters are first connected in series and then in parallel in a circuit across the same potential difference. The ratio of heat produced in series and parallel combinations would be :

1. 1:2
2. 2:1
3. 4:1
4. 1:4

Q. An electric heater of resistance $8\Omega$ draws $15A$ from the service mains $2$ hours. Calculate the rate at which heat is developed in the heater.

Q. When a 12V battery is connected across an unknown resistor, there is a current of 2.5 mA in the circuit. Find the value of the resistance of the resistor.

Q. The values of current I flowing in a given resistor for the corresponding values of potential difference V across the resistor are given below -

I(amperes)	0.5	1	2	3	4
V(volts)	1.6	3.4	6.7	10.2	13.2

Plot a graph between V and I and calculate the resistance of that resistor.

Q. Show how you would connect 3 resistors , each of resistance 6 ohm, so that the combination has a resistance of (i) 9 ohm (ii) 4 ohm

Q. Which uses more energy, a 250 W TV set in 1 hr, or a 1200W toaster in 10 minutes?

Q. How is a voltmeter connected in the circuit to measure the potential difference between two points?

Q. How many $176\Omega$ resistors (in parallel) are required to carry 5A on a 220V line?