A metal wire with constant resistance is fitted in an electric heater. To avoid overloading the heater circuit, the supply voltage is lowered from $230\ \text{V}$ to $220\ \text{V}$. Determine the percentage fall in the heater’s power output.
A uniform wire AB of length $100\ \text{cm}$ is joined between the terminals of a cell of e.m.f. $1.5\ \text{V}$ and negligible internal resistance, as shown in Fig. 6.1. An ammeter of internal resistance $5.0\ \Omega$ is attached to end A of the wire and to a movable contact C along the wire. Find the ammeter reading when contact C is placed (i) at A, (ii) at B.
Find the ammeter reading when contact C is placed at A.
Find the ammeter reading when contact C is placed at B.
Using the circuit in (b), record the ammeter reading $I$ for a range of distances $L$ of contact C from end A of the wire. Some points are already shown on Fig. 6.2.
Using your answers in (b), plot points on Fig. 6.2 for contact C at end A and at end B of the wire.
Draw a line of best fit through all the data points and hence find the ammeter reading when contact C is at the midpoint of the wire.
Use your answer in (ii) to calculate the potential difference between A and the contact C when the contact is at the midpoint of AB.
Explain why, even though contact C is at the midpoint of wire AB, the answer in (c)(iii) is not numerically equal to one half of the e.m.f. of the cell.