Current–Voltage Characteristics (AQA A Level Physics)

A filament lamp rated 15 V, 1.0 A has a resistance of 3.0 Ω when it carries no current. 

Figure 1

On the axes in Figure 1, sketch the form of the current against voltage characteristic for this lamp.

Explain why, as the voltage is increased either positively or negatively from zero, the characteristic has the form shown in your answer for part (a).

Using your answer from part (b), explain, in terms of electron flow how the resistance of the filament lamp changes as the current in the lamp increases.           

Figure 2 shows part the current-voltage (I-V) characteristic of a lamp up to its working voltage. 

Figure 2

Calculate the resistance in the lamp when 0.5 A of current is passed through it.

Figure 1

On Figure 1, sketch the I-V characteristic of a silicon semiconductor diode for forward bias.

Indicate approximate values on the voltage axis.

On Figure 1, sketch the I-V characteristic of a silicon semiconductor diode for reverse bias.

Indicate approximate values on the voltage axis.

Describe, with references to the characteristic you have drawn, how the resistance of the diode varies with the potential difference across its terminals for reverse bias and for forward bias.

A resistor and the semiconductor diode are connected in series with a variable power supply as shown in Figure 2.

Figure 2

Draw the I-V characteristic for the combination of the resistor and diode bias on Figure 3.

Figure 3

In a wire, 8.3 × 10¹⁵ electrons pass through a point in 45 s. 

Calculate the current that this represents.

A different wire carries a current of 50 mA. 

Calculate the number of electrons passing a point in this wire in 2.5 minutes.

In a test to find the suitable metal wire to use for a fuse, the following graph shown in Figure 1 of current, I, against time, t, was obtained. The circuit, which was connected to a constant source of emf, was switched on at t = 0 s. 

Figure 1

The maximum current through the wire before the fuse melted was 3.6 A. 

Calculate the total charge that flowed during this test.

The metal wire is then connected to a circuit with a 15 V cell. The total charge through the wire is equal to that during the fuse test.

Calculate the energy transferred in moving the total charge through the metal wire.

The current-voltage characteristic of a fixed resistor is shown in Figure 1. 

Figure 1

Calculate the resistance of the fixed resistor.

The fixed resistor is an example of an ohmic electrical component. 

Explain how Figure 1 shows that the resistor is an ohmic electrical component.

Sketch, on Figure 1, the current-voltage characteristic of a resistor with a larger resistance. Explain why you have drawn the graph in this way.

Calculate the work done by the charge flowing through the resistor when a current of 1.6 A flows through it in 1.5 minutes. 

In an attempt to investigate how the resistance of a filament lamp varies with current through a lamp, a student obtains the results shown in Table 1. 

Table 1

 Complete Table 1 by calculating the corresponding values of resistance to an appropriate number of significant figures.

Figure 1

On Figure 1, plot a graph of resistance against current for the filament lamp.

Using your graph from part (b), state and explain the relationship between the current and resistance in the filament lamp.

Hence, or otherwise, state and explain whether a filament lamp is an ohmic or non-ohmic conductor.

Figure 1 shows two electrons orbiting a helium nucleus with an orbital radius of 448 pm.  The total kinetic energy of the electrons in orbit is 4.61 × 10^–18 J. 

Figure 1

Calculate the size of the current created by the motion of the electrons orbiting the helium nucleus. 

When helium gas is placed between two electrodes with a high potential difference across them the helium atoms lose electrons and  ions are formed. 

The gas carries a current of 8.16 mA and the number of electrons passing any point in the gas per unit time is 2.58 × 10¹⁶ s^–1. 

Calculate the number of helium ions which will pass any point in the gas per unit time.

A cyclotron is used to accelerate charged particles outwards from the centre of a flat cylindrical vacuum chamber along a spiral path. 

During an experiment the cyclotron produces a beam of alpha particles which are directed towards a target.  The beam of alpha particles produces a current of 0.250 mA.  

Calculate how long it would take for 1 mole of alpha particles to strike the target.

A student wishes to determine the resistance for three different resistors. They connect the resistors in a ‘T’ arrangement and change the position of the power source and the voltmeter, as shown in Figure 1, to obtain two sets of results, as shown in Table 1. The power supply in Circuit 1 causes a current of 0.50 A 

Figure 1

Table 1

 Calculate the resistance of resistors ,  and .  

You may assume the voltmeter has an infinitely high resistance. 

A charge of 2 µC flows through a resistor when there is a potential difference of 4 V across it. 

Calculate the amount of electrical energy each electron will lose as it passes through the resistor and state what happens to this energy.

When investigating whether or not a resistor is an ohmic conductor state and explain which variable must be kept constant and how is this achieved.

An electron in a cathode ray tube is accelerated from rest through a potential difference of 150 kV and aimed towards a screen. 

Calculate the kinetic energy of the electrons when they collide with the screen.

If the current in the tube is 32 mA, calculate the rate at which the heat must be dissipated from the screen when it reaches its working temperature.

A travellator of width 50 cm has a surface containing a layer of electrons.  It moves through a brush, which collects the electrons and transports them away as electric current, at a speed of 5 m s^–1.  Figure 1 shows the arrangement of the conveyor belt and the brush.

Figure 1

Given that there are 10 000 electrons per mm² of the travellator, calculate the magnitude of the electric current through the wire brush.

Figure 1 shows the variation in the current flowing through a filament lamp after it has been switched on. 

Figure 1

Use Figure 1 to explain the variation of current flowing through the filament lamp after it has been switched on.

On Figure 1, draw the variation of current with time if the filament lamp had been stored at a colder temperature before being switched on.

Given that the filament lamp is 15% efficient, calculate the amount of light energy produced when the lamp is switched on for 30 minutes after being connected to a 12.0 V d.c supply. 

You can assume that the time taken to reach the normal operating temperature is negligible compared to the time the lamp is switched on for.

A beam of electrons, each of charge e, travels in a straight line with a uniform velocity, v.  

If the number of electrons per unit length of the beam is N, write an expression for the current produced by the beam in terms of N, e and v.

Four small identical conductors, each of charge +3e, are fixed on the edge of a circular insulating disc, as shown in Figure 1.The disc rotates at 100 revolutions per second.  

Figure 1

Calculate the magnitude of the charge of the electrical current at the edge of the disc.