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5. (10 pts.) The temperature of a copper wire (a = 3.9 x 10-'K') with a resistance of 100 is increased by 25 K (a) The resistance will increase or decrease? (b) What is the resistance after temperature increased by 25 K? 6. (10 pts.) A copper wire has a radius 0.5 mm and free electron density 8.5 x 10 and it carries current 1.8 A. Calculate the current density and the drift velocity of the copper wire. 4. = 1.602 x 10-1°C = 1.602 x 10-19A. 7. (5 pts.) Which combination of resistors has the highest equivalent resistance? emt R} R?RERS R2 A. (a) B. (b) C. (c) D. (d) E. the same (c) (d) 8. (5 pts.) A 100 W (1 Watt 1 Joule/s) light bulb is connected to a source of emf with Vem = 100 V. What is the resistance of the light bulb when the light bulb is operating? 9. (5 pts.) The product of R and C is called the time-constant RC. A capacitor is almost fully charged or fully discharged after about a time span of 4RC. Suppose we would like a 25 mF capacitor to be almost fully charged in 0.1 second. Determine the value of the resistance that we need to place in series with this capacitor when connected to a battery

Answer 1

here,

5)

the temperature coefficient of copper wire , alpha = 3.9 * 10^-3 K^-1

the initial resistance , R0 = 100 ohm

the change in temperature , dT = 25 degree

a)

as the temperature coefficient of copper is positive

the resistance will increase with increase in temperature

b)

the new resistance ,R = R0 * ( 1 + alpha * dT)

R = 100 * ( 1 + 3.9 * 10^-3 * 25) ohm

R = 109.75 ohm