Physics 9702/33 — October/November 2018

• Place the $15\ \Omega$ resistor in component holder P.
• Place the $22\ \Omega$ resistor in component holder Q.
• Set up the circuit shown in Fig. 1.1.

• K and L are crocodile clips.
The resistors in the component holders have resistances $P$ and $Q$.
Place L approximately half-way along the wire.
• The distance between K and L is $y$ as shown in Fig. 1.1.
Record $P$, $Q$ and $y$.

$P$ = ______
$Q$ = ______
$y$ = ______

• Close the switch.
• Record the ammeter reading $I$.

$I$ = ______

• Open the switch.

• Change one or both of the resistors in P and Q.
• Record the new values of $P$ and $Q$.

$P$ = ______
$Q$ = ______

• Close the switch.
• Change the position of L on the wire so that the ammeter reading is as close as possible to the value for $I$ in (a).
• Record $y$.

$y$ = ______

• Open the switch.

Repeat (b) until you have six sets of readings of $P$, $Q$ and $y$. Include your readings from (a) and (b).

Record your results in a table. Include values of $\frac{PQ}{P + Q}$ in your table.

It is suggested that the quantities $y$, $P$ and $Q$ are related by the equation

where $M$ and $N$ are constants.

Using your answers in (d)(iii), determine values for $M$ and $N$. Give appropriate units.

$M$ = ______
$N$ = ______

Theory suggests that

where $E$ is the electromotive force (e.m.f.) of the cell.

Calculate $E$. Give an appropriate unit.

$E$ = ______