1. A thin-walled metal sphere has a radius of 25 em and carries a charge of 2.0x

Question

1. A thin-walled metal sphere has a radius of 25 em and carries a charge of 2.0x107 c A point charge of -1.0x10 C is placed in the centre of the sphere. Find E for a point A point charge of -1.0x10 (a) inside the sphere, (b) just outside the sphere. ofa 3 m length of 20-mm iron wire is found to be 1.862. What is the 2. The resistance resistivity of iron? 3. (a) Find the equivalent resistance of three resistors (60, 50 and 40 ) connected in parallel. (b) If a potential difference of 12 V is applied across the combination, what is the current in each resistor? (c) How much lieat will be emitted in each resistor during 1 min?

Explanation / Answer

1. a. at a point just inside the sphere, E = 0

b. just outside the sphere E = KQ/r^2

E = 9e9 * 2e -7/(0.25*0.25)

E = 2.88 e4 N/C
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2. the formula for resistance R = rho L/A

resistivity rho = RA/L

rho = 1.8 * 3.14 * 10 e-3 * 10 e -3/3

rho = 1.88 e -4 Ohm m

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3a. in parallel:

1/Rnet = 1/R1 + 1/R2 +1/R3

1/Rnet = (1/60) + (1/50) + (1/40)

1/Rnet = 0.0616

Rnet = 16.21 ohms

3b. in parallel same volatge passes throught each of the ressistor

so

Current across 60 ohms = V/R = 12/60 = 0.2 Amps

Current across 50 ohms = V/R = 12/50 = 0.24 Amps

Current across 40 ohms = V/R = 12/40 = 0.3 Amps

Power P = Energy/time = V^2R = 12*12 * 16.21 = 2334.24 Watts

Energy E = 2334.24* 1* 60 = 1.4 e 5 Joules

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