2822 physics a june 2007

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.

MML 12544 1/06 T17344/6 © OCR 2007 [T/100/3701] OCR is an exempt Charity [Turn over

INSTRUCTIONS TO CANDIDATES

• 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.

FOR EXAMINER’S USE

Qu. Max. Mark

1 8

2 9

3 10

4 17

5 16

TOTAL 60

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Data

speed of light in free space, c = 3.00 × 108 m s–1

permeability of free space, �0 = 4� × 10–7 H m–1

permittivity of free space, �0 = 8.85 × 10–12 F m–1

elementary charge, e = 1.60 × 10–19 C

the Planck constant, h = 6.63 × 10–34 J s

unified atomic mass constant, u = 1.66 × 10–27 kg

rest mass of electron, me = 9.11 × 10–31 kg

rest mass of proton, mp = 1.67 × 10–27 kg

molar gas constant, R = 8.31 J K–1 mol–1

the Avogadro constant, NA = 6.02 × 1023 mol–1

gravitational constant, G = 6.67 × 10–11 N m2 kg–2

acceleration of free fall, g = 9.81 m s–2

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Formulae

uniformly accelerated motion, s = ut + 12 at 2

v2 = u2 + 2as

refractive index, n = 1sinC

capacitors in series, 1C

= 1C1

+ 1C2

+ . . .

capacitors in parallel, C = C1 + C2 + . . .

capacitor discharge, x = x0e–t/CR

pressure of an ideal gas, p = 13

NmV

<c2>

radioactive decay, x = x0e–λt

t 12 = 0.693

λ

critical density of matter in the Universe, ρ0 = 3H0

2

8�G

relativity factor, = √ (1 – v2

c2 )

current, I = nAve

nuclear radius, r = r0A1/3

sound intensity level, = 10 lg ( II0

)

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Answer all the questions.

1 (a) Fig. 1.1 shows the magnetic field pattern for a flat circular coil.

field lines

flat coil

d.c. supply

+

–

Fig. 1.1

Describe the change in the pattern of the magnetic field lines when the current in the coil is

(i) reversed

...........................................................................................................................................

..................................................................................................................................... [1]

(ii) increased in magnitude.

...........................................................................................................................................

..................................................................................................................................... [1]

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(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.

coulomb tesla ampere ohm [1]

[Total: 8]

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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.

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(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.

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..................................................................................................................................... [4]

(ii) At a particular temperature, the reading on the voltmeter is 3.6 V. Calculate the resistance of the thermistor at this temperature.

resistance = ..................................................... � [3]

[Total: 9]

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3 Fig. 3.1 shows the I-V characteristic of a particular electrical component.

I / AI / A0.070.07

0.060.06

0.050.05

0.040.04

0.030.03

0.020.02

0.010.01

0

0.07

0.06

0.05

0.04

0.03

0.02

0.01

0– 0.2 0.2 0 0 0.2 0.2 0.4 0.4 0.6 0.6 0.8 0.8 V / V– 0.2 0 0.2 0.4 0.6 0.8 V / V

Fig. 3.1

(a) Name the component.

............................................................................................................................................. [1]

(b) Circle the correct circuit symbol for the component. [1]

(c) Use Fig. 3.1 to calculate the resistance of the component at 0.20 V and 0.70 V.

resistance at 0.20 V = ..................................................... � [3]

resistance at 0.70 V = ..................................................... � [3]

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(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.

[2]

[Total: 10]

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4 (a) Name a quantity that has the same unit as potential difference or voltage.

............................................................................................................................................. [1]

(b) State the electrical unit defined as ‘a potential difference of 1 volt per ampere’.

............................................................................................................................................. [1]

(c) State the SI unit for electrical charge.

............................................................................................................................................. [1]

(d) State Kirchhoff’s first law.

...................................................................................................................................................

...................................................................................................................................................

............................................................................................................................................. [2]

(e) Fig. 4.1 shows an electrical circuit.

4.5 V

8.0 X

12 X

4.0 X

S1

S2

resistance wire

Fig. 4.1

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 �.

...........................................................................................................................................

..................................................................................................................................... [1]

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(ii) Calculate the resistivity of the material of the resistance wire.

resistivity = ................................... unit ………… [4]

(iii) When both switches are closed, calculate

1 the total resistance of the circuit

resistance = ..................................................... � [3]

2 the total electrical power delivered by the battery

power = ..................................................... W [3]

3 the ratio

current in the 12 � resistor ––––––––––––––––––––––– . current in the resistance wire

ratio = ......................................................... [1]

[Total: 17]

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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.

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............................................................................................................................................. [6]

Quality of Written Communication [2]

13


(c) In a laser beam, each photon has energy 2.0 eV.

(i) Show that the wavelength of the electromagnetic waves emitted by the laser is about 6 × 10–7 m.

[2]

(ii) Identify the region of the electromagnetic spectrum to which the waves emitted by the laser belong.

..................................................................................................................................... [1]

Question 5 is continued over the page.

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(d) Lithium ions are accelerated to a speed v. Fig. 5.1 shows a graph of the de Broglie wavelength

� of the ions against 1v

.

0 2 4 6 80 2 4 6 80 2 4 6 8

6

5

4

3

2

1

0

6

5

4

3

2

1

0

k / 1010–11–11mk / 10–11m

/ 1010–4–4s m–1–1I–V/ 10–4s m–11–V

Fig. 5.1

Determine the gradient of the graph of Fig. 5.1 and hence calculate the mass m of a single ion of lithium.

m = .................................................... kg [3]

[Total: 16]

END OF QUESTION PAPER

16

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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)


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

(d) p.d across diode = 0.75 (V) / (Rt = =060.0

5.4) 75 (Ω) C1

p.d across resistor = 4.5 – 0.75 = 3.75 (V) / (Rd = =060.075.0

) 12.5 (Ω) C1

63)5.62060.075.3( ≈==R (Ω) / R = (75 -12.5 = 62.5 ≈) 63 (Ω) 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]


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


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

(c)(i) E = 2.0 × 1.6 × 10-19 (= 3.2 × 10-19 J) C1

hfE = / λhcE = / f = 34

19

1063.6102.3

−

−

××

(= 4.83 × 1014 Hz))

19

834

102.3100.31063.6

−

−

××××

=λ / 14

8

1083.4100.3

××

=λ C1

λ = 6.22 × 10-7 (m) ≈ 6.2 × 10-7 (m) A0 (c)(ii) visible / ‘red’ (Allow: ‘light’) (No ecf allowed) B1 (d) gradient = 5.6(7) × 10-8 (Allow range: 5.5 × 10-8 to 5.9 × 10-8) B1

gradient = mh

/ 11-

-34

) vof value() of (value106.63

−××

=λ

m C1


16

m = 268

34

10)7(1.11067.51063.6 −

−

−

×=××

(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)

[Total: 16]

2822 physics a june 2007

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