Resistance (CIE A Level Physics)

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 B C D	2.0 4.0 6.0 8.0	1.5 3.2 1.9 0.9

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 I -V characteristics of two electrical components P and Q are shown below.

Which statement is correct ?

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

Two heating coils X and Y, of resistance R_X and R_Y respectively, deliver the same power when 12 V is applied across X and 6 V is applied across Y.

 What is the ratio   ?

A student found two unmarked resistors. To determine the resistance of the resistors, the circuit below was set up. The resistors were connected in turn between P and Q, noting the current readings.

 The voltage readings were noted without the resistors and with each resistor in turn.

The results were entered into a spreadsheet, as shown.

1.5	1.3	28	46
1.5	1.4	14	100

The student forgot to enter the column headings.

 Which order of the headings would be correct?

A	e.m.f / V V / V R / Ω I / mA
B	V / V e.m.f / V R / Ω I / mA
C	V / V e.m.f / V I / mA R / Ω
D	e.m.f / V V / V I / mA R / Ω

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 ?

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 diagram shows an electric pump for a garden fountain connected by an 18 m cable to a 230 V mains electrical supply.

The performance of the pump is acceptable if the potential difference (p.d.) across it is at least 218 V. The current through it is then 0.83 A.

 What is the maximum resistance per meter of each of the two wires in the cable if the pump is to perform acceptably?

The graph below shows the variation of the current I through a lamp with potential difference V across it.

Which of the following graphs best represents the variation of power P dissipated in the same lamp with I ² ?

Circuit contains three identical lamps A, B and C. Circuit also contains three switches, S₁, S₂ and S₃, as shown.

One of the lamps is faulty. In order to detect the fault, an ohm-meter is connected between terminals X and Y.

 When measuring resistance, the ohm-meter causes negligible current in the circuit. Readings of the ohm-meter for different switch positions are shown in the table.

Switch			Meter reading / Ω
S1	S2	S3
open closed open open	open open closed closed	open open open closed	∞ 15 30 15

Which lamps are faulty?

The current flowing through a component varies with the potential difference V across it as shown.

Which graph best represents how the resistance R varies with V ?

The circular cross-sectional area of a uniform metal wire varies along its length. There is a current in the wire. The narrow end of the wire is at a reference potential of zero.

Which graph best represents the variation with distance x along the wire of the potential difference V relative to the reference zero?

The graph shows the I -V characteristics of a semiconductor diode

A cell of e. m .f. 1.2 V and negligible internal resistance is connected in series to a semiconductor diode and a resistor R₁, as shown below

A resistor R₂ of resistance 375 Ω is connected across the cell. The diode has the characteristic shown in the graph. The current supplied by the cell is 7.6 mA.

 What is the resistance of R₁?

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

Which row of the table gives the resistance of the component at V₂ and describes how the resistance changes from V₁ to V₂ ?

	Resistance at V2	Change in resistance from V1 to V2
A		increases
B		decreases
C		increases
D		decreases

The graph shows the relationship between potential difference V and current I for a fixed 20 Ω resistor and a filament lamp.

The resistor and lamp are placed in series with a 9 V battery of negligible internal resistance. What is the current in the circuit ?

The graphs show the I -V characteristics for a metal conductor and a thermistor

What is the ratio   ?

One style of light bulb, very different from the "incandescent" design which works on the principle of a super-heated wire filament emitting light, is called a gas discharge tube.

 In this design of light bulb, light is produced by the direct excitation of gas molecules as electric current passes between two electrodes.

What will the I - V graphs of these bulbs look like?