EMF PAG

Question 1

Equipment

Answer 1

● Battery or cell
● Voltmeter
● Ammeter
● Variable resistor
● Switch

Question 2

Method

Answer 2

2. Set the variable resistor to its maximum value.
3. Close the switch and record voltage from the voltmeter
   and the current from the ammeter, open the switch
   between readings to prevent heating of the variable
   resistor.
4. Decrease the resistance of the variable resistor and
   repeat this, obtaining pairs of readings of V and I over the
   widest possible range.

Question 3

Calculations

Answer 3

● ε = I(R + r) = V + Ir ⇒ V = − rI + ε , this is in the form y=mx+c (a straight line graph)
● Plot a graph of V against I and draw a line of best fit. The y-intercept will be the emf
and the gradient will be the negative internal resistance.