A current of $200 \mathrm{~mA}$ flows through a $4 \mathrm{k} \Omega$ resistor. What is the p.d. across the resistor?

Given:

R =  $4 \mathrm{k} \Omega = 4000 \Omega$

I = $200 \mathrm{~mA} = 0.2 A$

To find:

the potential difference, V

Solution:

According to ohm's law:

$V=I \times R$

$V=0.2 \times 4000$

$V=800 \ volt$

The  p.d. across the resistor is 800 volt.