IGCSE Physics 0625 Paper 4 Practice Paper: Waves, Sound, Light and the Electromagnetic Spectrum (Extended Theory, 100 marks)

Level: Year 10-11 (IGCSE) | Subject: Physics 0625 | Time: 60 minutes | Total: 100 marks | Parts: 36

Paper at a glance

Paper	Time	Marks	Calculator
Paper 4 (Extended, structured)	1 h 15 min	75	Not allowed

Questions

Question 1 (16 marks) – Basic wave quantities and the wave equation

(a) Define wavelength. (2 marks)

(b) A sound wave has frequency 50 Hz and wavelength 6.8 m. Calculate its speed. (3 marks)

(c) The speed of sound in air is 340 m/s and a note has frequency 850 Hz. Calculate its wavelength. (3 marks)

(d) A radio wave travels at 3.0 x 10^8 m/s with frequency 1.0 x 10^8 Hz. Calculate its wavelength. (3 marks)

(e) A vibration has frequency 50 Hz. Calculate its period. (3 marks)

(f) Give one example each of a transverse wave and a longitudinal wave. (2 marks)

Question 2 (17 marks) – Reflection, refraction and total internal reflection

(a) State the two parts of the law of reflection. (2 marks)

(b) A ray strikes a plane mirror at an angle of incidence of 30 degrees. Calculate the angle between the incident ray and the reflected ray. (3 marks)

(c) Light passes from air into water (refractive index 1.33) at an angle of incidence of 40 degrees. Calculate the angle of refraction to one decimal place. (3 marks)

(d) A glass has refractive index 1.50. Calculate its critical angle to one decimal place. (3 marks)

(e) Explain how an optical fibre uses total internal reflection to carry a signal from one end to the other. (3 marks)

(f) The speed of light in a vacuum is 3.0 x 10^8 m/s. Calculate the speed of light in water (refractive index 1.33). (3 marks)

Question 3 (17 marks) – Sound, echoes and ultrasound ranging

(a) Explain why sound cannot travel through a vacuum. (2 marks)

(b) A student claps 170 m from a wall. The speed of sound is 340 m/s. Calculate the time until the echo is heard. (3 marks)

(c) A ship sends an ultrasound pulse to the seabed and receives the echo 0.040 s later. The speed of sound in sea water is 1500 m/s. Calculate the depth. (3 marks)

(d) State the frequency range of human hearing and define ultrasound. (3 marks)

(e) A car sounding its horn moves towards a stationary observer. State how the pitch heard changes and explain why. (3 marks)

(f) Suggest two ways of reducing noise inside a classroom. (3 marks)

Question 4 (17 marks) – The electromagnetic spectrum: properties and uses

(a) Arrange these waves in order of increasing frequency: X-rays, infrared, radio waves, ultraviolet, visible light. (2 marks)

(b) Visible light of frequency 6.0 x 10^14 Hz. Calculate its wavelength in nm. (3 marks)

(c) A microwave oven operates at 2.45 x 10^9 Hz. Calculate the wavelength in cm to one decimal place. (3 marks)

(d) State one benefit and one danger of ultraviolet radiation to humans. (3 marks)

(e) Give two everyday uses of infrared radiation. (3 marks)

(f) Explain why X-rays are used for medical imaging and state one safety precaution. (3 marks)

Question 5 (17 marks) – Lenses and image formation

(a) Explain how a converging lens brings a beam of parallel rays to a focus. (2 marks)

(b) A converging lens has focal length 10 cm. An object is placed 30 cm from the lens. Calculate the image distance. (3 marks)

(c) For the lens in part (b), calculate the magnification. (3 marks)

(d) The same object is now placed 6 cm from the lens. State three properties of the image. (3 marks)

(e) Explain how a diverging lens corrects short sight. (3 marks)

(f) A camera lens has focal length 12 cm and the object is 20 cm away. Calculate the magnification. (3 marks)

Question 6 (16 marks) – Energy in waves, power and applications

(a) A wave doubles in amplitude. State how its energy changes and explain why. (3 marks)

(b) Solar radiation of intensity 800 W/m2 falls on a 2.0 m2 panel of efficiency 20 percent. Calculate the output power. (3 marks)

(c) An observer moves twice as far from a point source of light. How does the intensity received change, and why? (3 marks)

(d) An appliance rated at 2000 W runs for 1.5 hours. Calculate the energy used in kWh. (3 marks)

(e) State one advantage of digital signals over analogue signals. (2 marks)

(f) Give two advantages of optical fibre communication over copper cable. (2 marks)

Answers and marking notes

Question 1 – Basic wave quantities and the wave equation

(a) The distance between two consecutive points in phase, for example two adjacent crests. [2 marks]

(b) v = f x wavelength = 50 x 6.8 = 340 m/s (one mark equation, one mark multiplication, one mark unit). [3 marks]

(c) wavelength = v / f = 340 / 850 = 0.40 m (one mark equation, one mark value, one mark unit). [3 marks]

(d) wavelength = 3.0 x 10^8 / 1.0 x 10^8 = 3.0 m. [3 marks]

(e) T = 1 / f = 1 / 50 = 0.020 s (one mark equation, one mark value, one mark unit). [3 marks]

(f) Transverse: light (or water waves). Longitudinal: sound. [2 marks]

Question 2 – Reflection, refraction and total internal reflection

(a) The angle of incidence equals the angle of reflection, and the incident ray, reflected ray and normal lie in the same plane. [2 marks]

(b) Angle of reflection = 30 degrees; 180 – 30 – 30 = 120 degrees (one mark reflected angle, one mark geometry, one mark answer). [3 marks]

(c) sin r = sin 40 / 1.33 = 0.643 / 1.33 = 0.483, so r = 28.9 degrees (one mark equation, one mark sine value, one mark angle). [3 marks]

(d) sin c = 1 / 1.50 = 0.667, so c = 41.8 degrees. [3 marks]

(e) Light inside the core meets the core-cladding boundary at an angle greater than the critical angle, so total internal reflection occurs and the light travels along the core with very little energy loss. [3 marks]

(f) v = 3.0 x 10^8 / 1.33 = 2.26 x 10^8 m/s (one mark equation, one mark value, one mark power and unit). [3 marks]

Question 3 – Sound, echoes and ultrasound ranging

(a) Sound is a longitudinal wave and needs particles of a medium to pass on the vibration; a vacuum has no particles, so sound cannot travel through it. [2 marks]

(b) The sound travels there and back, 2 x 170 = 340 m; t = 340 / 340 = 1.0 s (one mark return path, one mark calculation, one mark unit). [3 marks]

(c) Total distance 1500 x 0.040 = 60 m, so depth = 60 / 2 = 30 m (one mark multiplication, one mark halving, one mark unit). [3 marks]

(d) 20 Hz to 20 000 Hz; sound with a frequency above 20 000 Hz is called ultrasound. [3 marks]

(e) The pitch rises: the moving source compresses the waves ahead of it, so the wavelength reaching the observer is shorter and the frequency, hence the pitch, is higher. [3 marks]

(f) Fit sound-absorbing panels to walls and ceiling; close doors and windows, limit the volume of equipment or wear ear defenders. [3 marks]

Question 4 – The electromagnetic spectrum: properties and uses

(a) Radio waves, infrared, visible light, ultraviolet, X-rays. [2 marks]

(b) wavelength = 3.0 x 10^8 / 6.0 x 10^14 = 5.0 x 10^-7 m = 500 nm (one mark equation, one mark metre value, one mark conversion). [3 marks]

(c) wavelength = 3.0 x 10^8 / 2.45 x 10^9 = 0.122 m = 12.2 cm. [3 marks]

(d) Benefit: it helps the skin make vitamin D. Danger: it causes sunburn and premature skin ageing, and overexposure increases the risk of skin cancer. [3 marks]

(e) Remote controls for televisions and air conditioners; thermal imaging cameras, night vision or infrared thermometers. [3 marks]

(f) X-rays pass through soft tissue but are absorbed by denser material such as bone, so an image is formed; staff wear lead aprons, radiographs are only taken when necessary and exposure time is kept short. [3 marks]

Question 5 – Lenses and image formation

(a) Parallel rays are refracted towards the principal axis at both surfaces and meet at the principal focus. [2 marks]

(b) 1/f = 1/u + 1/v, so 1/v = 1/10 – 1/30 = 1/15 and v = 15 cm (one mark equation, one mark substitution, one mark answer). [3 marks]

(c) m = v / u = 15 / 30 = 0.50, so the image is diminished, inverted and real. [3 marks]

(d) 1/v = 1/10 – 1/6 = -1/15, so v = -15 cm: the image is virtual, upright and magnified (magnification 2.5). [3 marks]

(e) In a short-sighted eye parallel rays focus in front of the retina; a diverging lens spreads the rays so that they focus further back, on the retina. [3 marks]

(f) 1/v = 1/12 – 1/20 = 2/60, so v = 30 cm and m = 30 / 20 = 1.5 (one mark image distance, one mark equation, one mark answer). [3 marks]

Question 6 – Energy in waves, power and applications

(a) The energy becomes four times greater, because the intensity of a wave is proportional to the square of its amplitude. [3 marks]

(b) Input power 800 x 2.0 = 1600 W; output 1600 x 0.20 = 320 W (one mark input, one mark efficiency, one mark unit). [3 marks]

(c) The intensity falls to one quarter, because the same energy is spread over four times the area. [3 marks]

(d) 2000 W = 2.0 kW; 2.0 x 1.5 = 3.0 kWh (one mark conversion, one mark multiplication, one mark unit). [3 marks]

(e) Digital signals are more resistant to interference and can be stored, compressed and reproduced exactly with little loss over long distances. [2 marks]

(f) Much greater bandwidth and speed; low signal loss and no interference from electromagnetic fields. [2 marks]

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