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The diode used in the circuit shown in the figure has a constant voltage drop of 0.5V at all currents and a maximum power rating 100mW. What should be the value of the resistor R connected in series with the diode for obtaining maximum current

A) 1.5 ohm

B) 5 ohm

C) 6.67 ohm

D) 200 ohm

- Diode's Voltage Drop, Vd = 0.5V

- Maximum Power Rating, P = 100mW = 0.1 Watts

- Battery EMF, E = 1.5V

- Resistance = R

1) Finding Current in the Circuit:

So it's given E = 1.5V and Vd = 0.5V

Formula: P = I*Vd => I = (P/Vd)

I = (0.1/0.5)

= 0.2A

2) Finding Potential Drop Across R

V = E – Vd

= 1.5 - 0.5

= 1V

3) Finding Value of R

From above, V = 1V and I = 0.2 A

V = IR

R = V / I

= 1 / 0.2

= 5 ohms

Hence the answer is B. :)

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