5. Consider the Earth and a cloud layer 600 m above the planet to be the plates

Question

5. Consider the Earth and a cloud layer 600 m above the planet to be the plates of a paralel-plate capacitor. The cloud layer has an area of 2.0X10' m2: What is the capacitance? 6. A 120 V heater is rated at 1200 watts. What is the current through the heater? 7. A metallic conductor has a resistivity of 15 x10*Om. What is the resistance of a piece that is 30m long and has a uniform cross sectional area of 6.5 X10 m2 8. What will the new resistance be of a 250 0 platinum wire if its temperature is raised from 20c to 92°C? 9. When a resistor is connected across a 12.0-V battery, a current of 482 x10 Amp flows. What is the resistance in the circuit?

Explanation / Answer

5.

Capacitance is given by:

C = e0*A/d

C = 8.85*10^-12*2*10^5/600

C = 2.95*10^-9 F

C = 2.95 nF

6.

Power is given by:

P = V*i

i = P/V = 1200/120

i = 10 Amp

7.

Resistance is given by:

R = rho*L/A

R = 15*10^-6*30/(6.5*10^-6)

R = 69.23 ohm

8.

R = R0*(1 + alpha*dT)

R = 250*(1 + 3.73*10^-3(92 - 20))

R = 317.14 ohm

9.

R = V/i = 12/(482*10^-3)

R = 24.90 ohm

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