7.) A charge of 4.2 C of charge passes through a pocket calculator’s solar cells

Question

7.) A charge of 4.2 C of charge passes through a pocket calculator’s solar cells in 3.7 h. What is the power output in mW, given the calculator’s voltage output is 3.4 V?

8.) What is the resistance of a 22.7 m long piece of copper wire having a 1.918 mm diameter? (Resistivity of copper is 1.72 x 10-8 m).

9.)

During open-heart surgery, a defibrillator can be used to bring a patient out of cardiac arrest. The resistance of the path is 479.6 and a 13.7 mA current is needed. What voltage should be applied?

Explanation / Answer

Given that

charge q=4.2 c

time t=3.7 h=3.7*3600=13320 sec

voltage V=3.4 v

now we find the power output

power P=4.2*3.4/13320

=1.1 mW

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(8) ans

Given that

length L=22.7 m

diameter D=1.918 mm

radius r=0.959*10^-3 m

resistivity of copper =1.72*10^-8 ohm*m

now we find the resistance

resistance R=1.72*10^-8*22.7/(3.14*(0.959*10^-3)^2

=13.5 *10^-2 ohm

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(9) ans

Givewn that

current i=13.7 mA

resistance R=479.6 ohm

basing on ohms law

now we find the voltage should be applied

voltage V=13.7*10^-3*479.6=6.6 v

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