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ADVANCED SUBSIDIARY GCE UNIT 2822PHYSICS A
Electrons and Photons
FRIDAY 8 JUNE 2007 Morning
Time: 1 hourAdditional materials:
Electronic calculator
This document consists of 15 printed pages and 1 blank page.
• Write your name, Centre Number and Candidate number in the boxes above.• Answer all the questions.• Use blue or black ink. Pencil may be used for graphs and diagrams only.• Read each question carefully and make sure you know what you have to do before starting your answer.• Do not write in the bar code.• Do not write outside the box bordering each page.• WRITE YOUR ANSWER TO EACH QUESTION IN THE SPACE PROVIDED. ANSWERS WRITTEN
ELSEWHERE WILL NOT BE MARKED.
INFORMATION FOR CANDIDATES
• The number of marks for each question is given in brackets [ ] at the end of each question or part question.
• The total number of marks for this paper is 60.• You will be awarded marks for the quality of written communication where this
is indicated in the qustion.• You may use an electronic calculator.• You are advised to show all the steps in any calculations.
(b) The force experienced by a current-carrying conductor placed at right angles to a uniform magnetic field may be determined using Fleming’s left-hand rule. On Fig. 1.2, identify the directions of the magnetic field, the conventional current and the force experienced by the conductor by inserting the words field, current and force in the boxes.
Fig. 1.2 [2]
(c) The force F experienced by a current-carrying conductor placed at right angles to a magnetic field is given by the equation
F = BIL.
Identify the labels used in this equation.
B ...............................................................................................................................................
I ................................................................................................................................................
L .......................................................................................................................................... [3]
(d) Underline the correct electrical unit below that is defined in terms of the force between two current-carrying conductors.
2 (a) On Fig. 2.1, sketch the variation with temperature of the resistance of a pure metallic conductor.
resistance
0
0 100 temperature / oC
Fig. 2.1 [2]
(b) Fig. 2.2 shows a circuit used to monitor the changes in the temperature of a room.
A
V
5.0 V
1200 X
Fig. 2.2
The thermistor is connected in series with a resistor of fixed value 1200 �. The battery has e.m.f. 5.0 V and negligible internal resistance. Assume that the ammeter has negligible resistance and the voltmeter has very high resistance.
(i) The thermistor is a negative temperature coefficient (NTC) thermistor. State and explain the changes in the ammeter and voltmeter readings as the temperature of the thermistor is increased.
(d) Fig. 3.2 shows the component with the I-V characteristic shown in Fig. 3.1 connected in series with a resistor of resistance R and a supply of e.m.f. 4.5 V.
4.5 V
R
component with the I-Vcharacteristic shown in Fig. 3.1
0.060 A
Fig. 3.2
The supply has negligible internal resistance. The current in the resistor is 0.060 A.
Use Fig. 3.1 to determine the resistance R of the resistor.
R = ..................................................... � [3]
(e) On the axes of Fig. 3.1, draw the I-V characteristic of a metallic conductor kept at a constant temperature and having the same resistance as your answer to (d). Label your line M.
The battery has e.m.f. 4.5 V and has negligible internal resistance. The resistance wire has resistance 4.0 �, length 15 cm and cross-sectional area 2.3 × 10–8 m2.
(i) Suggest how you can arrange switches S1 and S2 (e.g. opened or closed) so that the circuit has a total resistance of 12 �.
5 (a) Two of the most important equations from quantum physics are listed below.
equation 1 E = hf
equation 2 � = hmv
Complete the following sentences:
(i) Equation 1 describes the ………………… behaviour of electromagnetic waves. [1]
(ii) Equation 2 describes the ………………… behaviour of a particle such as an electron. [1]
(b) In this question two marks are available for the quality of written communication.
A negatively charged metal plate is illuminated by light. Electrons escape from the metal when blue light of weak intensity is used. No electrons are released when weak or intense red light is used. Use the ideas of the photoelectric effect to explain these observations.
Permission to reproduce items where third-party owned material protected by copyright is included has been sought and cleared where possible. Every reasonable effort has been made by the publisher (OCR) to trace copyright holders, but if any items requiring clearance have unwittingly been included, the publisher will be pleased to make amends at the earliest possible opportunity.
OCR is part of the Cambridge Assessment Group. Cambridge Assessment is the brand name of University of Cambridge Local Examinations Syndicate (UCLES), which is itself a department of the University of Cambridge.
2822/01 Mark Scheme June 2007
12
1 (a)(i) The field is reversed / down (the page) (AW) B1 (a)(ii) There are more field lines / lines are closer (Not ‘stronger field’) B1 (b) Correct terms in boxes. (‘Clockwise’: force/motion: field : current) B2 (Two items correct: 1/2 Only one item correct: 0/2) (c) B : (magnetic) flux density (Allow ‘(magnetic) field strength’) B1 I : current B1 L : length (of conductor) in the field B1 (d) ampere B1
[Total: 8] 2 (a) Finite resistance at 0o C B1 Resistance increases B1 (b)(i) Any four from:
1. The resistance of the thermistor decreases (as temperature is increased) B1 2. The total resistance (of circuit) decreases B1 3. The voltmeter reading increases B1
4. Explanation of 3. above in terms of ‘sharing voltage’ / 2
1
2
1
RR
VV
= / 021
2 VRR
RV ×+
= B1
5. The current increases / ammeter reading increases B1
6. Explanation of current increase in terms of totalRVI = B1
(Allow ecf for statements 3. and 5. if statement 1. is incorrect – maximum score of 2/4)
2822/01 Mark Scheme June 2007
13
(b)(ii) )100.3(1200
6.3 3−×==I / 2
1
2
1
RR
VV
= / 021
2 VRR
RV ×+
= C1
3100.34.1
−×=R /
6.34.1
1200=
R / 0.5
12004.1 ×
+=
RR
C1
R = 467 (Ω) ≈ 470 (Ω) A1 (When 1.4 V and 3.6 V are interchanged, then R = 3.1 × 103 (Ω) can score 2/3) (Calculation of total circuit resistance of 1.67 × 103 (Ω) can score 2/3)
(Use of 1200
0.5=I scores 0/3)
[Total: 9]
3 (a) (Semiconductor) diode B1 (b) The diode symbol circled (No ecf allowed) B1
(c) IVR = C1
At 0.20 V, R = infinite / very large A1
At 0.70 V, 35)020.070.0( ==R (Ω) (Allow answers in the range: {31.82 to 38.89}) A1
(Use of 0.70 V across the diode gives R = 63.3Ω - This can score 2/3) (e) Straight line through the origin M1 Line of correct gradient (with line passing through 0.63 V, 0.01 A) [Possible ecf] A1
[Total: 10]
2822/01 Mark Scheme June 2007
14
4 (a) Electromotive force /e.m.f. B1 (b) ohm / (1) Ω B1 (c) Coulomb / C B1 (d) The sum of the currents entering a point / junction is equal to the sum of the currents
leaving (the same point) Or ‘Algebraic sum of currents at a point = 0’ B2 (-1 for the omission of ‘sum’ and -1 for omission of ‘point’/ ‘junction’)
(Do not allow 4321 IIII +=+ unless fully explained) (e)(i) S2 closed and S1 open. B1
(e)(ii) ALR ρ
= (Allow any subject) C1
15.0
103.20.4 8−××==
LRAρ C1
ρ = 6.133 × 10-7 ≈ 6.1 × 10-7 (Answer of 6.1 × 10-9 can score 2/3) A1 unit: Ω m B1
(e)(iii)1. 21
111RRR
+= / 21
21
RRRRR
+= C1
resistance of parallel combination = 0.30.4120.412
=+×
(Allow 1 SF) C1
total resistance = 8.0 + 3.0 = 11 (Ω) A1
(e)(iii)2. R
VP2
= / 4091.0(11/5.4 ==I A) C1
115.4 2
=P / 114091.0 2 ×=P or 4091.05.4 ×=P C1
8.184.1 ≈=P (W) (Possible ecf from (iii)1.) A1
2822/01 Mark Scheme June 2007
15
(e)(iii)3. ratio = 33.0)12
0.40.4/
12/( ==VV
/ ratio = 31
/ 1:3 B1
[Total: 17] 5 (a)(i) particle / particulate / quantum / photon B1 (a)(ii) wave B1 (b) Any three from points 1 to 6:
1. Photon mentioned B1 2. Surface electrons are involved B1 3. A single photon interacts with a single electron B1 4. Energy is conserved in the interaction between photon and electron B1 5. (max)KEhf += φ M1 6. hf is the energy of the photon, φ is the work function (energy) and KE(max) is the
(maximum) kinetic energy of the electron. A1 The frequency of blue light is greater than the red light / the wavelength of blue light is shorter than the red light (ora) B1 The photon of blue light has energy greater than the work function energy / the frequency of blue light is greater than the threshold frequency (ora) B1 Intensity does not change the energy of a photon B1
QWC The answer must involve physics, which attempts to answer the question.
Structure and organisation - Award this mark if the whole answer is well structured. B1
Spelling and Grammar mark - More than two spelling mistakes or more than two grammatical errors means the SPAG mark is lost. B1
(kg) /m in the range: 1.1 × 10-26 to 1.2 × 10-26 (kg) A1
(Possible ecf for the last two marks) (The 10-4 factor is not very clear on the v-1 axis; therefore allow full credit for using 104. This gives a gradient of 5.7 × 10-16 and mass m of 1.17 × 10-18 kg)