May/June 2025 Paper 41 Worked Answers (IGCSE Physics 0625 Extended)

10 questions · 80 marks · 75 minutes

Question papers and mark schemes are copyright Cambridge International. We do not reproduce them: the worked answers here are written by The Practice Book. Have the paper open alongside. Get the official paper from Cambridge

1. Question 1

   1 marksDistance from a speed-time graph
   Distance is the area under a speed-time graph. The motion has three sections: a triangle for the acceleration phase, a rectangle for the constant-speed phase, and a triangle for the deceleration phase. Area = (1/2 x 100 x 60) + (60 x 300) + (1/2 x 100 x 60) = 3000 + 18 000 + 3000 = 24 000 m.
   Method:

   Compute the triangle, rectangle and triangle areas and add them: 3000 + 18 000 + 3000 = 24 000 m.
   Examiner tips

   • For trapezium-shaped speed-time graphs, split the area into a rectangle and two triangles.

2. Question 2

   1 marksEffects of a resultant force
   A resultant force on a moving object produces an acceleration. That acceleration can change the size of the velocity (the speed) and/or the direction of the velocity. It does not change the mass, temperature or density of the object.
   Method:

   Recall that resultant force causes acceleration, changing speed and/or direction.
   Examiner tips

   • A resultant force changes velocity, which means speed and/or direction.

3. Question 3

   1 marksWork done against gravity
   Work done against gravity = weight times height = m times g times h = 65 x 9.8 x 2.8 = 1784 J, which rounds to about 1800 J.
   Method:

   Compute m g h = 65 x 9.8 x 2.8 = 1784 J, rounded to 1800 J.
   Examiner tips

   • Work done lifting a mass equals the gravitational potential energy gained: m g h.

4. Question 4

   1 marksCurrent from electrical power
   Power P = current I times voltage V, so current = power divided by voltage = 2000 W divided by 230 V = 8.7 A.
   Method:

   I = P / V = 2000 / 230 = 8.7 A.
   Examiner tips

   • Always work in SI units: convert kW to W before using P = I V.

5. Question 5

   1 marksRefraction at an air-soap boundary
   Refractive index n equals the sine of the angle of incidence divided by the sine of the angle of refraction. So the sine of the refraction angle equals the sine of 60 degrees divided by 1.28, which is 0.866 / 1.28 = 0.677. The refraction angle is therefore about 43 degrees.
   Method:

   Use n = sine i / sine r, find sine r = sine 60 / 1.28 = 0.677, then r is about 43 degrees.
   Examiner tips

   • Light bends towards the normal when entering a denser medium, so r < i.

6. Question 6

   1 marksMaterial for a permanent magnet
   Steel is a hard magnetic material that, once magnetised, retains its magnetism, so it makes a good permanent magnet. Soft iron loses its magnetism easily and is used for temporary magnets such as transformer cores. Copper and plastic are not magnetic.
   Method:

   Choose steel because it stays magnetised once magnetised.
   Examiner tips

   • Steel = hard magnetic = permanent magnet; soft iron = temporary magnet.

7. Question 7

   1 marksResistance from voltage and current
   Resistance = voltage divided by current = 230 V divided by 3.9 A = about 59 ohms.
   Method:

   Apply R = V / I = 230 / 3.9 = about 59 ohms.
   Examiner tips

   • Always check whether the question asks for V/I or I/V.

8. Question 8

   1 marksTransformer turns ratio
   For an ideal transformer the turns ratio equals the voltage ratio: Ns divided by Np equals Vs divided by Vp. So Ns = Np x Vs / Vp = 450 x 300 000 / 25 000 = 5400 turns.
   Method:

   Apply Ns / Np = Vs / Vp to get Ns = 450 x 300 000 / 25 000 = 5400 turns.
   Examiner tips

   • For an ideal transformer, the turns ratio equals the voltage ratio.

9. Question 9

   1 marksBeta decay of strontium-90
   In beta-minus decay, a neutron in the nucleus changes into a proton and an electron, and the electron is emitted as the beta particle. The proton number rises by 1 (from 38 to 39, so the element becomes yttrium) and the nucleon number stays the same at 90.
   Method:

   Apply beta-minus rules: proton number 38 to 39, nucleon number stays 90, giving yttrium-90.
   Examiner tips

   • Beta-minus decay: proton number plus 1, nucleon number unchanged.

10. Question 10

    1 marksOrbital speed in the Solar System
    The Sun's gravitational field strength is greater closer to the Sun. A planet at a smaller orbital radius needs to travel faster to stay in a circular orbit. Earth is much closer to the Sun than Jupiter, so its orbital speed is greater.
    Method:

    Earth is closer to the Sun, where gravity is stronger, so it must orbit faster than Jupiter.
    Examiner tips

    • Closer to the Sun means stronger gravity and higher orbital speed.