Mark Scheme February assessment

1.       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 I1 + I2 = I3 + I4 unless fully explained)

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  2.     A:   gamma / γ (ray/radiation/wave)                                                                        B1
       λ = 10–16 to 10–10 (m)                                                                                       B1
B:    infrared / IR / i.r.                                                                                              B1
       λ = 7 × 10–7 to 10–3 (m)                                                                                    B1

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  3.     (i)      v   = I / nAe = 0.0025 / (8.5 × 1028 × 1.1 × 10–7 × 1.6 × 10–19) (1)
     = 1.67 × 10–6 m s–1 (1)                                                                                2

  (ii)   Free electron concentration (or wtte) is much smaller in the thermistor than
in the wire.                                                                                                       1

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  4.     (a)     R = R1 + R2 / R = 200 + 120 / R = 320                                                            C1
current =                                                                                                 C1
current = 2.5 ´ 10–2 (A)                                                                                 A0

  (b)   V = 25 ´ 10–3 ´ 120 / V =
V = 3.0 (V)                (Possible ecf)                                                                B1

  (c)   p.d. across the 360 (W) resistor = p.d. across the 120 (W) resistor /
There is no current between A and B / in the voltmeter                                 B1
(Allow ‘A & B have same voltage’ - BOD)

          The p.d. calculated across 360 W resistor is shown to be 3.0 V /
The ratio of the resistances of the resistors is shown to be the same.             B1

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  5.     (i)      plane polarised light vibrates (travels) in one plane only                                B1
(look for reference to one plane of oscillation)

(ii)     only transverse waves can be polarised/AW                                                  B1
sound waves are longitudinal/not transverse/AW                                           B1

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6.       (a)     (i)      amplitude = 3.75 cm {allow 3.7 to 3.8)                                                B1

(ii)     when t = 1.8 ms displacement = ANY negative value                           B1

(–)3.35 cm (ALLOW 3.3 TO 3.4)                                                         B1

(iii)    period = 2.64 ms (allow 2.64 to 2.68)                                                   B1

(iv)    frequency = 1/period                                                                            C1

= 1/(2.64 × 10 – 3) = 379 Hz (379 to 373 or 380) {ecf for T}              A1

  (b)   recall of v = fl                                                                                               C1

l = v/f = 300/379 = 0.79 m (or 0.8 m) {allow ecf from (iv)}                         A1

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  7.     Any three properties from:                  (–1 for each error or contradiction)        B1 ´ 3

1.      Travel at the speed of light / c / 3 ´ 108 m s–1 (NOT ‘same speed’)

2.      Travel through vacuum / ‘free space’

3.      Have oscillating electric and magnetic fields

4.      They are (all) transverse waves / can be polarised

5.      Allow: ‘They show diffraction / reflection / refraction / interference’

6.      Allow: ‘Consist of photons’

Any three regions from the list below:                                                               B1 ´ 3

Gamma (rays / radiation) / g (rays) ; X-rays ; u.v ; ir ; microwaves ; radio waves

(NOT ‘radio’)

One suitable application for the opted region.                                                         B1

(E.g.: Gamma rays for radiotherapy / sterilisation;

X-rays for taking pictures of skeleton / bones; u.v for tanning; ir for TV remote
control; microwaves for cooking / mobile phones; radio waves for communication)

(Note: Reference to alpha, beta and gamma can only score the last marking point)

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  8.     (i)      evidence of knowledge of:
full/max transmission when the (transmission axis of) polarising sheet is
parallel to the light’s plane of polarisation/vibrations                                     B1
no transmission when the (transmission axis of) polarising sheet is at right
angles to light’s plane of polarisation/vibrations                                            B1

(ii)     reflected light from surface is partially plane polarised                                  B1
polarising sheet is placed at right angles to reflected light’s polarisation        B1
plane/AW

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  9.       (b)                                                    (Allow other subject, with or without D)     C1
(charge =) 7800 ´ 0.23                                                                                            C1
1.794 ´ 103 » 1.8 ´ 103 (C)                                                  (Ignore minus sign)     A1
(1.8 ´ 106 (C) scores 2/3)

(c)     (number =)           (Possible ecf)                                                    C1
(number =) 1.12 ´ 1022 » 1.1 ´ 1022                                                              A1

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