Current-voltage characteristicsAQA A-Level Physics: Mind map

Exam questions on Current-voltage characteristics

1. A student investigates a fixed resistor kept at a constant temperature, using an ideal ammeter and an ideal voltmeter. She records a pd of 2.0 V with a current of 4.0 mA, a pd of 4.0 V with a current of 8.0 mA, and a pd of 6.0 V with a current of 12.0 mA. She plots a graph with pd on the vertical axis and current on the horizontal axis.
   Calculate the resistance of the resistor at 2.0 V and at 6.0 V, and state what the results show about the resistor.2 marks
2. Two components, X and Y, are connected in turn to a variable power supply, with an ideal ammeter and an ideal voltmeter. For each component a graph is plotted of pd (vertical axis) against current (horizontal axis). The graph for X is a straight line through the origin with a gradient of 40 Ω. The graph for Y is a curve through the origin whose gradient increases as the current increases.
   X is a metal wire. State the condition needed for X to obey Ohm's law, and explain what would happen to the graph for X if the current became large enough to make the wire very hot.2 marks
3. A technician tests a semiconductor diode with an ideal ammeter and an ideal voltmeter. In the forward direction the current is negligible at 0.50 V, 2.0 mA at 0.70 V and 20 mA at 0.75 V. In the reverse direction, with 5.0 V across the diode, the current is 0.10 μA.
   Describe how the current in the diode varies with pd in the forward and reverse directions.3 marks