Everything Science Grade 11

19.3 CHAPTER 19. ELECTRIC CIRCUITS

Step 2 : Determine how to approach the problem.

We can use Ohm’s Lawto find the total resistance R in the circuit, and then

calculate the unknown resistance using:

R = R 1 + R 2

because it is in a series circuit.

Step 3 : Find the total resistance

V = R· I

∴ R =

V

I

=

1 , 5

0 , 25

= 6Ω

Step 4 : Find the unknown resistance

We know that:

R = 6Ω

and that

R 1 = 1Ω

Since

R = R 1 + R 2

R 2 = R− R 1

Therefore,

R 2 = 5Ω

Batteries and internal resistance ESBIM

Real batteries are madefrom materials which have resistance. This means that real batteries are not
just sources of potentialdifference (voltage), butthey also possess internal resistance. If the total
voltage source is referred to as the emf,E, then a real battery canbe represented as an emf connected
in series with a resistor r. The internal resistanceof the battery is represented by the symbol r.

E

r

R

V