Q. 4

# A heater coil is to be constructed with a nichrome wire (ρ = 1.0 × 10^{–8} Ω m) which can operate at 500 W when connected to a 250 V supply.

(a) What would be the resistance of the coil?

(b) If the cross-sectional area of the wire is 0.5 mm^{2}, what length of the wire will be needed?

(c) If the radius of each turn is 4.0 mm, how many turns will be there in the coil?

Answer :

(a) Let *R* be the resistance of the coil.

Given, resistivity, ρ = 1.0 × 10^{–8} Ω m

The power *P* consumed by a coil of resistance *R* when connected across a supply *V* is given by Joule’s heating effect-

(b) We know resistance R is given by-

where

ρ = resistivity of the material

l = length of the wire

A= area of cross section of the wire

Given, cross-sectional area of the wire is 0.5 mm^{2}

(c) Let *n* be the number of turns in the given coil.

Given, radius of each turn is 4.0 mm

Then,

Where,

l = length of the coil

r=radius of the coil

Rate this question :

An electric bulb marked 220 V, 100 W will get fused if it is made to consume 150 W or more. What voltage fluctuation will the bulb withstand?

HC Verma - Concepts of Physics Part 2A servo voltage stabilizer restricts the voltage output to 220 V ± 1%. If an electric bulb rated at 220 V, 100 W is connected to it, what will be the minimum and maximum power consumed by it?

HC Verma - Concepts of Physics Part 2Figure shows an electrolyte of AgCl through which a current is passed. It is observed that 2.68 g of silver is deposited in 10 minutes on the cathode. Find the heat developed in the 20Ω resistor during this period. Atomic weight of silver is 107.9 g mol^{–1}.

HC Verma - Concepts of Physics Part 2

Find the charge required to flow through an electrolyte to liberate one atom of (a) a monovalent material and (b) a divalent material.

HC Verma - Concepts of Physics Part 2Find the thermo-emf developed in a copper-silver thermocouple when the junctions are kept at 0°C and 40°C. Use the data in table (33.1).

HC Verma - Concepts of Physics Part 2The coil of an electric bulb takes 40 watts to start glowing. If more than 40 W is supplied, 60% of the extra power is converted into light and the remaining into heat. The bulb consumes 100 W at 220 V. Find the percentage drop in the light intensity at a point if the supply voltage changes from 220 V to 200 V.

HC Verma - Concepts of Physics Part 2