## Explain the following

[question] Question. Explain the following : (1)Why is tungsten used almost exclusively for filament of incandescent lamps ? (2)Why are the conductors of electric heating devices, such as toasters and electric irons, made of an alloy rather than a pure metal ? (3)Why is the series arrangement not used for domestic circuits ? (4)How does the resistance of a wire vary with its cross-sectional area ? (5)Why are copper and aluminium wires usually employed for electricity transmission ? [/question] [...

## An electric heater of resistance $8 \Omega$ draws $15 \mathrm{~A}$ from the service mains for 2 hours.

[question] Question. An electric heater of resistance $8 \Omega$ draws 15 A from the service mains for 2 hours. Calculate the rate at which heat is developed in the heater. [/question] [solution] solution: Here, $\mathrm{I}=15 \mathrm{~A}, \mathrm{R}=8 \Omega, \mathrm{t}=2 \mathrm{~h}$ Rate at which heat is developed, i.e, electric power, $\mathrm{P}=\mathrm{I}^{2} \mathrm{R}=(15)^{2} \times 8=1800 \mathrm{~W}$ [/solution]...

## Which uses more energy,

[question] Question. Which uses more energy, a $250 \mathrm{~W}$ TV set in $1 \mathrm{~h}$, or a $1200 \mathrm{~W}$ toaster in 10 minutes ? [/question] [solution] solution: Energy used by $250 \mathrm{~W}$ TV set in $1 \mathrm{~h}=250 \times 1=250 \mathrm{Wh}$ Energy used by $1200 \mathrm{~W}$ toaster in $10 \mathrm{~min}$. (i.e., $1 / 6 \mathrm{~h})=1200 \times(1 / 6)=200 \mathrm{Wh}$ Thus, a $250 \mathrm{~W}$ TV set uses more energy in $1 \mathrm{~h}$ than a $1200 \mathrm{~W}$ toaster in 10 mi...

## Two lamps, one rated 100 W at 220 V

[question] Question. Two lamps, one rated $100 \mathrm{~W}$ at $220 \mathrm{~V}$, and the other $60 \mathrm{~W}$ at $220 \mathrm{~V}$, are connected in parallel to the electric mains supply. What current is drawn from the line if the supply voltage is 220 V ? [/question] [solution] solution: Resistance of first lamp, $R_{1}=\frac{V^{2}}{P}=\frac{(220)^{2}}{100}$ resistance of the second lamp, $\mathrm{R}_{2}=\frac{\mathrm{V}^{2}}{\mathrm{P}}=\frac{(220)^{2}}{60}$ Since the two lamps are connecte...

## Which of the following terms does not represent electrical power in a circuit ?

[question] Question. Which of the following terms does not represent electrical power in a circuit ? (1) $I^{2} R$ (2) $\mathrm{IR}^{2}$ (3) VI (4) $\mathrm{V}^{2} / \mathrm{R}$ [/question] [solution] solution: Electrical power, $\mathrm{P}=\mathrm{VI}=(\mathrm{IR}) \mathrm{I}=\mathrm{I}^{2} \mathrm{R}$ $\mathrm{P}=\mathrm{V} \mathrm{I}=\mathrm{V}\left(\frac{\mathrm{V}}{\mathrm{R}}\right)=\frac{\mathrm{V}^{2}}{\mathrm{R}}$ Obviously, $\mathrm{IR}^{2}$ does not represent electrical power in a cir...

## What determines the rate at which energy

[question] Question. What determines the rate at which energy is delivered by a current ? [/question] [solution] solution: Electric power determines the rate at which energy is delivered by a current. [/solution]...

## An electric iron of resistance

[question] Question. An electric iron of resistance $20 \Omega$ takes a current of 5 A. Calculate the heat developed in $30 \mathrm{~s} .$ [/question] [solution] solution: Here, resistance, $R=20 \Omega$, current, $I=5 A$, time, $t=30 \mathrm{~s}$. Heat produced, $\mathrm{H}=\mathrm{I}^{2} \mathrm{R} \mathrm{t}=(5)^{2} \times 20 \times 30$ $=1.5 \times 10^{4} \mathrm{~J}$ [/solution]...

## Define the SI unit of current.

[question] Question. Define the SI unit of current. [/question] [solution] solution: The SI unit of current is ampere (A). Current flowing through a conductor is said to be 1 ampere if 1 coulomb of charge flows through it in 1 second. [/solution]...

## What does an electric circuit mean ?

[question] Question. What does an electric circuit mean ? [/question] [solution] solution: An electric circuit is a closed and continuous path consisting of many devices like resistors, electric bulbs, etc. through which an electric current flows. [/solution]...