Notes Ask Your T A wire of resistance 4.0 a is connected to a battery whose emf

Question

Notes Ask Your T A wire of resistance 4.0 a is connected to a battery whose emf is 3.0 V and whose internal resistance is 1.0 . (a) How much energy is transferred from chemical to electrical form in 4.0 min? (b) How much energy appears in the wire as thermal energy in that time? 2. My Notes Ask Your When electric usage approaches the maximum available supply, power companies may resort to a "brown-out" and reduce the supplied voltage Normally a household voltage is 120 V. (a) what is the resistance of a 60 w bulb under normal conditions? ohm (b) In a brown out, suppose the voltage is reduced by 10% to 108 V. What is the power of the bulb now? (c) By what % has the power decreased? % (d)To solve this problem you had to assume that something remained constant. What was it? (This is not a perfect approximation, but it is a starting point.) O Power of bulb Current in bulb O Resistance of bulb

Explanation / Answer

1) We know that current in the circuit, I = total emf/ total resistance = E/(R+r)

R = external resistance = 4

r = internal resistance of the cell = 1

E = emf of cell = 3 V

THEN I = 3/5 = 0.6 amps

t = time = 4 min = 240 sec

a) energy transferred from chemical to electrical, U1 = EIt = 3*0.6*240 = 432 J

b) energy dissipated as thermal energy in the wire, U2 = I2R*t = (0.6)2*4*240 = 345.6 J

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