Question

The capacitor in the flash of a disposable camera has a value of 165 μF. 1) What is the resistance of the filament in the bulb if it takes 10 s to charge the capacitor to 80% of its maximum charge? (Express your answer to two significant figures.)

Answer 1

Answer:

3.8 x 10⁴ Ω

Explanation:

C = Capacitance = 165 μF

R = resistance of the filament = ?

t = time taken to charge the capacitor = 10 s

Q₀ = maximum charge stored by capacitor

Q = charge stored by capacitor at time "t" = 0.80 Q₀

T = Time constant

Charge stored by capacitor at any time is given as

$Q = Q_{o}(1 - e^{\frac{-t}{T}})$

$0.80 Q_{o} = Q_{o}(1 - e^{\frac{-10}{T}})$

T = 6.21 s

Time constant is given as

T = RC

6.21 = R (165 x 10⁻⁶)

R = 3.8 x 10⁴ Ω