A-LevelPhysicsWaves9702/23 · Oct/Nov 2020 · Q16 Marks

Answer all the questions in the spaces provided. (a) An electromagnetic wave has a wavelength of 85 µm.

(a)(i)State the wavelength, in m, of the wave. wavelength = .............................................................. m [1][1]
(a)(ii)Calculate the frequency, in THz, of the wave. frequency = ........................................................... THz [2][2]
(a)(iii)State the name of the region of the electromagnetic spectrum that contains this wave. [1][1]
(b)The current I in a coil of wire produces a magnetic field. The energy E stored in the magnetic field is given by E = I²L / 2 where L is a constant. The manufacturer of the coil states that the value of L, in SI base units, is 7.5 × 10⁻⁶ ± 5%. The current I in the coil is measured as (0.50 ± 0.02) A. The values of L and I are used to calculate E. Determine the percentage uncertainty in the value of E. percentage uncertainty = ...................................................... % [2][2]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2020). The mark or mark type is shown in brackets.

[1] wavelength = 8.5 × 10⁻⁵ m
[1] f = v/λ or c/λ
[1] = 3.0 × 10⁸ / 8.5 × 10⁻⁵ (= 3.5 × 10¹²)
[1] = 3.5 THz
[1] infrared
[1] (implied) percentage uncertainty in I = 4% or (implied) fractional uncertainty in I = 0.04
[1] percentage uncertainty in E = 5% + (4% × 2)
[1] = 13%

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