B M Sharma Solutions for Chapter: Heating Effects of Current, Exercise 2: Concept application Excercise

A fuse with a circular cross-sectional radius of $0.15 \mathrm{m}\mathrm{m}$ blows at $15 \mathrm{A}$. What should be the radius of the cross section of a fuse made of the same material that blows at $30 \mathrm{A}$?

A motor operating on $120 \mathrm{V}$ draws a current of $2 \mathrm{A}$. If the heat is developed in the motor at the rate of $9 \mathrm{c}\mathrm{a}\mathrm{l} {\mathrm{s}}^{-1}$, what is its efficiency?

The walls of a closed cubical box of edge $40 \mathrm{c}\mathrm{m}$ are made of a material of thickness $1 \mathrm{m}\mathrm{m}$ and thermal conductivity $4\times {10}^{-4} \mathrm{c}\mathrm{a}\mathrm{l} {\mathrm{s}}^{-1} \mathrm{c}{\mathrm{m}}^{-1} °{\mathrm{C}}^{-1}$. The interior of the box is maintained at $100° \mathrm{C}$ above the outside temperature by a heater placed inside the box and connected across $400 \mathrm{V}$ d.c. Calculate the resistance of the heater.

Two tungsten lamps with resistances $R_1$ and $R_2$ respectively, are connected first in parallel and then in series in a lighting circuit of negligible internal resistance. Given that $R_1>R_2$
(a) Which lamp will glow more brightly when they are connected in parallel?

(b) If the lamp of resistance $R_1$ now burns out, how will the net illumination produce change?

(c) Which lamp will glow more brightly when they are connected in series?

(d) If the lamp of resistance $R_2$ now bums out and lamp $R_1$, alone is plugged in, will the net illumination increase or decrease?

$n$ identical bulbs are connected in series and illuminated by a power supply. One of the bulbs gets fused. The fused bulb is removed and the remaining bulbs are again illuminated by the same power supply. Find the fractional change in the illumination of all the bulbs.

$n$ identical bulbs are connected in series and illuminated by a power supply. One of the bulbs gets fused. The fused bulb is removed and the remaining bulbs are again illuminated by the same power supply. Find the fractional change in the illumination of one bulb.

An electric motor is designed to work at $100 \mathrm{V}$ and draws a current of $6 \mathrm{A}$. The output power supplied by the motor is $150 \mathrm{W}$, and the remaining goes to heat. What is the resistance of the windings of the motor and its percentage efficiency?

A voltage stabilizer restricts the voltage output to $200 \mathrm{V}\pm 1 \mathrm{\%}$. If the electric bulb rated $220 \mathrm{V}$, $100 \mathrm{W}$ is connected to it, what will be the minimum and maximum power consumed by it?