Current–Voltage Characteristics (AQA A Level Physics)

A charge of 8.0 C passes through a resistor of resistance 30 Ω at a constant rate in a time of 20 s.

What is the potential difference across the resistor?

The graph shows how current I varies with voltage V for a filament lamp.

Since the graph is not a straight line, the resistance of the lamp varies with V.

Which row gives the correct resistance at the stated value of V?

	V / V	R / Ω
A	2.0	1.5
B	4.0	3.2
C	6.0	1.9
D	8.0	0.9

The potential difference across a component in a circuit is 2.0 V.

How many electrons must flow through this component in order for it to be supplied with 4.8 J of energy?

A milliammeter shows a reading of 20 mA.

How many electrons flow through the milliammeter in 10 seconds?

The resistance R of a resistor is to be determined. The current I in the resistor and the potential difference V across it are measured.

The results, with their uncertainties, are

                                    I = (2.0 ± 0.2) A                     V = (15.0 ± 0.5) V

What is the uncertainty in this value for R?

The current in the circuit shown is 4.8 A

What is the direction of flow and the rate of flow of electrons through the resistor R?

	direction of flow	rate of flow
A	X to Y	3.0 × 1019 s–1
B	X to Y	6.0 × 1018 s–1
C	Y to X	3.0 × 1019 s–1
D	Y to X	6.0 × 1018 s–1

The variation with potential difference V of the current I in a semiconductor diode is shown below.

What is the resistance of the diode for applied potential differences of +1.0 V and –1.0 V?

	resistance at +1.0 V	resistance at –1.0 V
A	20 Ω	infinite
B	20 Ω	zero
C	0.05 Ω	infinite
D	0.05 Ω	zero

A battery of negligible internal resistance is connected to two 10 Ω resistors in series.

What charge flows through each of the 10 Ω resistors in 1 minute?

The graph shows the voltage-current graph of a filament wire.

What is the resistance of the wire when it obeys Ohm’s law?

The diagram shows a length of track from a model railway connected to a battery, a resistor and a relay coil.

With no train present, there is a current in the relay coil which operates a switch to turn on a light.

When a train occupies the section of track, most of the current flows through the wheels and axles of the train in preference to the relay coil. The switch in the relay turns off the light.

Why is a resistor placed between the battery and the track?

The graph shows how the potential difference V across an electrical component varies with current I in the component.

A tangent has been drawn on the curve at point P for a current of I₂.

What is the resistance of the electrical component when the current in the component is I₂?

The simple series circuit is set up and the terminal voltage of the supply is set to 6 V. The bulb has an efficiency of 80% and over a period of 10 s, 450 J of light energy is recorded as emitted by the bulb.

What is the resistance of the bulb?

The speed of electrons in a conductor can be calculated using the equation

                                                      I = nAve

where I is the current in A, n is the number of electrons per m³, A is the cross sectional area in m², v is the average velocity of electrons in m s^–1 and e is the charge on one electron which is 1.6 × 10^–19 C.

The circuit below is set up to measure the speed of electrons in copper.

For copper, n = 8.5 × 10²⁸ per m³.

The voltage of the supply is 12 V and the diameter of the wire is 2.4 mm. In 10 seconds, the wire transforms 240 J of electrical energy into heat energy.

 What is the average velocity of the electrons in the wire?

A 2 Ω resistor and a 4 Ω resistor are connected to a cell.

Which graph shows how the potential V varies with distance between X and Y?

A resistor and a diode are connected in parallel and connected to a d.c. supply.

What is the correct graph of current against voltage for the circuit?

In biology, there is a field called electrophysiology. This is where charged ions of sodium (Na⁺) and potassium (K⁺) pass through cell membranes creating a potential difference between the two sides of the cell. Nerve cells work on this principle and allow transmission of messages using action potentials.

We can plot an approximate graph of the sodium and potassium components of the cell’s current and voltage characteristic. The lines on this graph show the potassium component and the overall I-V curve.

Which of the following sketch graphs could represent the I-V characteristic for the Na⁺ ion?

The following circuit is built including a charge carrying copper wire of length 1 m and mass 72 grams.

The wire hovers in a horizontal magnetic field of magnitude 0.23 T when  a current passes through it. A horizontal magnetic field will produce a vertical force on a charge carrying wire.

 The force on the wire can be found using the equation

                                                                     F = 

 Where F is force in N, B is magnetic field strength in T, I is the current in A and is the length of the wire in metres.

 A current flows in this wire for 0.4 mins.

 What is the charge transferred in this time?

Resistivity,, is a property that describes the extent to which a material opposes the flow of electric current through it. It can be calculated using the equation

                                                                    = 

Where R is the resistance in Ohms, A is the cross sectional area of the wire in m² and L is the length of the material in m.

Which of the following cannot be the units for resistivity?

A circuit contains an LED and a thermistor connected in series and powered by a 9V DC supply.

The I-V characteristic of the LED is shown in this graph

The resistance vs temperature relationship for the thermistor are shown in the second graph below

The light from the LED becomes visible when the current through it is 0.28 A. 

What is the temperature when the LED turns on?

The figure below shows the current-voltage characteristic for a photovoltaic solar cell.

 Two of these cells are connected in parallel to power a circuit.

 If circuit is operating at 5.5 V, what percentage of the maximum possible power is being used?