In an experiment to verify Ohm’s law, a student is provided with a dry cell, a rheostat, a known resistor R, a key, connecting wires, an ammeter, and a voltmeter.
(i) Draw a clearly labelled circuit diagram for the experiment showing the correct placement of the ammeter and the voltmeter.
(ii) Explain why the ammeter used in the circuit must have a very low resistance. How does this property help in obtaining an accurate I–V graph?
(iii) Let the resistance of the ammeter be rA. Show that the effective resistance of the circuit becomes R+rA when the ammeter is connected, and hence explain how the slope of the V–I graph is affected.
(iv) If R=5Ω and rA=0.5Ω, calculate the percentage error in the slope of the V–I graph that will arise if rA is ignored.