Question 4
4
A battery of electromotive force 12 V and negligible internal resistance is connected to two resistors and a light-dependent resistor (LDR), as shown in Fig. 4.1. An ammeter is connected in series with the battery. The LDR and switch S are connected across the points XY .
structured2 marks
Question 4(a)
4(a)
The switch S is open. Calculate the potential difference (p.d.) across X Y.
Mediumstructured0 marks
Answer
total resistance \(=20(\mathrm{k} \Omega) \quad \mathrm{C} 1\) current = 12 / \(20(\mathrm{~mA})\) or potential divider formula C1 p.d. \(=[12 / 20] \times 12=7.2 \mathrm{~V}\) A1 [3]
Question 4(c)
4(c)
The switch S remains closed. The intensity of the light on the LDR is increased. State and explain the change to
structured2 marks
Question 4(c)(ii)
4(c)(ii)
the p.d. across XY .
Mediumstructured2 marks
Answer
resistance across XY is less M1 less proportion of 12 V across XY hence p.d. is less A1
Question 5
5
Fig. 5.1 shows a 12 V power supply with negligible internal resistance connected to a uniform metal wire AB . The wire has length 1.00 m and resistance \(10 \Omega\). Two resistors of resistance \(4.0 \Omega\) and \(2.0 \Omega\) are connected in series across the wire. Currents \(I_{1}, I_{2}\) and \(I_{3}\) in the circuit are as shown in Fig. 5.1.
structured0 marks
Question 5(b)
5(b)
Calculate the potential difference (p.d.) between the points C and D , as shown in Fig. 5.1. The distance A C is 40 cm and D is the point between the two series resistors.
Mediumstructured0 marks
Answer
p.d. \(B C: 12-12 \times 0.4=7.2(V) /\) p.d. \(A C=4.8(V) \quad C 1\) p.d. \(B D: 12-12 \times 4 / 6=4.0(V) /\) p.d. \(A D=8.0(V) \quad C 1\) p.d. \(=3.2 \mathrm{~V}\) A1
Question 5
5
A uniform resistance wire A B has length 50 cm and diameter 0.36 mm . The resistivity of the metal of the wire is \(5.1 \times 10^{-7} \Omega \mathrm{~m}\).
structured2 marks
Question 5(b)
5(b)
The wire A B is connected in series with a power supply E and a resistor R as shown in Fig. 5.1. The electromotive force (e.m.f.) of E is 6.0 V and its internal resistance is negligible. The resistance of R is \(2.5 \Omega\). A second uniform wire C D is connected across the terminals of E. The wire C D has length 100 cm , diameter 0.18 mm and is made of the same metal as wire A B. Calculate
structured2 marks
Question 5(b)(iii)
5(b)(iii)
the potential difference (p.d.) between the midpoint M of wire AB and the midpoint N of wire CD. p.d. = V
Hardstructured2 marks
Answer
potential drop A to M = 1.25 × 1.2 \(=1.5 \mathrm{~V} \quad\) M1 potential drop C to \(\mathrm{N}=3.0 \mathrm{~V}\) p.d. \(\mathrm{MN}=1.5 \mathrm{~V}\)
Question 6
6
2 marks
Question 6(b)
6(b)
The ends B and D of the wire in (a) are connected to a cell X, as shown in Fig. 6.1. The cell X has electromotive force (e.m.f.) 2.0 V and internal resistance \(1.0 \Omega\). A cell Y of e.m.f. 1.5 V and internal resistance \(0.50 \Omega\) is connected to the wire at points B and C , as shown in Fig. 6.1. The point C is distance l from point B . The current in cell Y is zero. Calculate
structured2 marks
Question 6(b)(iii)
6(b)(iii)
the distance l.
Mediumstructured2 marks
Answer
p.d. across \(\mathrm{BC}(l)=1.5(\mathrm{~V}) \quad \mathrm{C} 1\)
Question 6
6
7 marks
Question 6(b)
6(b)
A uniform wire AB of length 100 cm is connected between the terminals of a cell of e.m.f. 1.5 V and negligible internal resistance, as shown in Fig. 6.1. An ammeter of internal resistance \(5.0 \Omega\) is connected to end A of the wire and to a contact C that can be moved along the wire. Determine the reading on the ammeter for the contact C placed
structured1 marks
Question 6(b)(i)
6(b)(i)
at A ,
Mediumstructured0 marks
Answer
zero A1
Question 6(b)(ii)
6(b)(ii)
at B . reading =
Mediumstructured1 marks
Answer
0.3(0) A A1
Question 6(c)
6(c)
Using the circuit in (b), the ammeter reading I is recorded for different distances L of the contact C from end A of the wire. Some data points are shown on Fig. 6.2.
structured4 marks
Question 6(c)(i)
6(c)(i)
Use your answers in (b) to plot data points on Fig. 6.2 corresponding to the contact C placed at end A and at end B of the wire.
Mediumstructured1 marks
Answer
correct plots to within \(\pm 1 \mathrm{~mm} \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots . . \quad\) B1
Question 6(c)(ii)
6(c)(ii)
Draw a line of best fit for all of the data points and hence determine the ammeter reading for contact C placed at the midpoint of the wire. reading = A
Mediumstructured1 marks
Answer
reasonable line/curve through points giving current as 0.12 A allow \(\pm 0.005 A\) ) B1
Question 6(c)(iii)
6(c)(iii)
Use your answer in (ii) to calculate the potential difference between A and the contact C for the contact placed at the midpoint of AB . potential difference = V
Mediumstructured2 marks
Answer
V=I R \(V=0.12 \times 5.0\) =0.6(0) V
Question 6(d)
6(d)
Explain why, although the contact C is at the midpoint of wire AB , the answer in (c)(iii) is not numerically equal to one half of the e.m.f. of the cell.
Hardstructured2 marks
Answer
circuit acts as a potential divider/current divides/current in AC not the same as current in BC resistance between A and C not equal to resistance between C and B....... B1 or current in wire \(\mathrm{AC} \times \mathrm{R}\) is not equal to current in wire \(\mathrm{BC} \times \mathrm{R} \quad \mathrm{B} 1\) any 2 statements
Question 5
5
3 marks
Question 5(b)
5(b)
The variable resistor in (a) is now connected as a potential divider, as shown in Fig. 5.3. Calculate the maximum possible and minimum possible current \(I_{2}\) in the ammeter.
Mediumstructured2 marks
Answer
maximum current \(=2.0 \mathrm{~A}\) minimum current =0 A1 A1 [2]
Question 5(c)
5(c)
1 marks
Question 5(c)(ii)
5(c)(ii)
The resistor of resistance \(6.0 \Omega\) is replaced with a filament lamp in the circuits of Fig. 5.1 and Fig. 5.3. State an advantage of using the circuit of Fig. 5.3, compared to the circuit of Fig 5.1, when using the circuits to vary the brightness of the filament lamp.
Mediumstructured1 marks
Answer
B1 [1]
Question 5
5
2 marks
Question 5(c)
5(c)
A cell of e.m.f. 2.0 V and negligible internal resistance is connected to a variable resistor R and a metal wire, as shown in Fig. 5.1. The wire is 900 mm long and has an area of cross-section of \(1.3 \times 10^{-7} \mathrm{~m}^{2}\). The resistance of the wire is \(3.4 \Omega\).
structured2 marks
Question 5(c)(ii)
5(c)(ii)
The resistance of R may be varied between 0 and \(1500 \Omega\). Calculate the maximum potential difference (p.d.) and minimum p.d. possible across the wire. maximum p.d. = V minimum p.d. = V
Mediumstructured2 marks
Answer
\(\max =2 .(0) \mathrm{V}\) \(\min =2 \times(3.4 / 1503.4)=4.5 \times 10^{-3} V\)
Question 6
6
A battery is connected in a circuit with a light-dependent resistor (LDR), two fixed resistors and a voltmeter, as shown in Fig. 6.1. The battery has an electromotive force (e.m.f.) of 25 V and negligible internal resistance. The resistors have resistances of \(320 \Omega\) and \(240 \Omega\).
structured6 marks
Question 6(a)
6(a)
The voltmeter displays a reading of 16 V .
structured3 marks
Question 6(a)(ii)
6(a)(ii)
Calculate the resistance of the LDR. resistance = \(\Omega\)
Mediumstructured3 marks
Answer
\[ R=(25-16) / 0.050 \] or \[ R=(9 / 16) \times 320 \] or \[ R=(25 / 0.050)-320 \] C1 \(R=180(\Omega)\) C1 \[ \begin{aligned} R_{(\mathrm{LDR})} =[(1 / 180)-(1 / 240)]^{-1} =720 \Omega \end{aligned} \] A1 or \[ \begin{aligned} I =(25-16) / 240 (=0.0375 \mathrm{~A}) \end{aligned} \] (C1) \[ \begin{aligned} I_{(\mathrm{LDR})} =0.050-0.0375 (=0.0125 \mathrm{~A}) \end{aligned} \] (C1) \[ \begin{aligned} R_{(\mathrm{LDR})} =9.0 / 0.0125 =720 \Omega \end{aligned} \] (A1)
Question 6(b)
6(b)
The intensity of the light incident on the LDR increases. State and explain what happens to the voltmeter reading.
Mediumstructured3 marks
Answer
resistance of LDR decreases B1 resistance of parallel combination decreases or total resistance (of circuit) decreases or current in resistor of resistance \(320 \Omega\) increases or potential difference across parallel combination / LDR / \(240 \Omega\) resistor decreases M1 voltmeter reading increases A1
Question 33
33
Which circuit results in output voltage \(V_{\text {out }}\) increasing with increasing temperature?
Mediummcq1 marks
Answer
C
Question 33
33
A conductor consists of three wires connected in series. The wires are all made of the same metal but have different cross-sectional areas. There is a current I in the conductor. Point Y on the conductor is at zero potential. Which graph best shows the variation of potential V with distance along the conductor?
Mediummcq1 marks
Answer
A