A torch bulb is rated 5V and 500mA. Calculate its (i) power, (ii) resistance, (iii) energy consumed when it is lighted for 4 hours.

Given: A torch bulb is rated 5V and 500mA.

To find: (i) power, (ii) resistance, (iii) energy consumed when it is lighted for 4 hours

Solution:

(i) Power:

$Power = Voltage \times Current$  or P = VI

We know, 500 mA = 0.5 A

So, $power =  5 \times 0.5 = 2.5$

Power = 2.5 watt

(ii) Resistance:

According to Ohm's law, $Resistance \ (R) = \frac{Voltage \ (V)}{Current \ (I)}$

So, $R = \frac{5}{0.5} = 10$

Resistance = 10 ohm

(iii) Energy consumed for 4 hours:

We know, $Energy = Power \times Time$

Time = 4 hours

Converting into seconds, we get $4 \ hours = 4 \times 60 \times 60 \ seconds$

So, $Energy = 2.5 \times 4 \times 60 \times 60 \ seconds$

= 36,000

Energy consumed in 4 hours is $3.6 \times 10^4 \ joule$

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Updated on: 10-Oct-2022

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