Question 15 Marks
a. Define Power and state its SI unit.
b. A torch bulb is rated 5 V and 500 mA . Calculate its
i. Power
ii. Resistances
iii. Energy consumed when it is lighted for $2 \frac{1}{2}$ hours.
b. A torch bulb is rated 5 V and 500 mA . Calculate its
i. Power
ii. Resistances
iii. Energy consumed when it is lighted for $2 \frac{1}{2}$ hours.
Answer
View full question & answer→a. Power is defined as rate of doing work/ rate at which energy is consumed/ rate at which electric energy is dissipated in an electric circuit. In simpler terms, it measures how quickly energy is converted from one form to another or how quickly work is done.
S.I unit of Power is watt
i. $\mathrm{P}=$ VI
$=5$ volt $\times 500 \mathrm{~mA}$
$=5$ volt $\times \frac{500}{1000} \mathrm{~A}$
$=2.5$ watt
ii. $\mathrm{P}=\frac{V^{2}}{R}$
or $\mathrm{R}=\frac{5 \text { volt } \times 5 \text { volt }}{2.5 \text { watt }}$
$\mathrm{R}=\frac{250}{25}=10 \Omega$
iii. Energy Consumed $=$ Power $\times$ Time
$=2.5 \mathrm{~W} \times 2.5 \mathrm{~h}$
$=6.25 \mathrm{~Wh}$
S.I unit of Power is watt
i. $\mathrm{P}=$ VI
$=5$ volt $\times 500 \mathrm{~mA}$
$=5$ volt $\times \frac{500}{1000} \mathrm{~A}$
$=2.5$ watt
ii. $\mathrm{P}=\frac{V^{2}}{R}$
or $\mathrm{R}=\frac{5 \text { volt } \times 5 \text { volt }}{2.5 \text { watt }}$
$\mathrm{R}=\frac{250}{25}=10 \Omega$
iii. Energy Consumed $=$ Power $\times$ Time
$=2.5 \mathrm{~W} \times 2.5 \mathrm{~h}$
$=6.25 \mathrm{~Wh}$
