AQA AS LEVEL JUNE 2025 PHYSICS 7407/ 1 PAPER 1 MARK
SCHEME
Exam
Section 1: Particles and Radiation
1. Define specific charge and calculate it for a proton.
Answer:
Specific charge = charge/mass
For proton: charge = +1.60 × 10⁻¹⁹ C, mass = 1.67 × 10⁻²⁷
kg
Specific charge = (1.60 × 10⁻¹⁹)/(1.67 × 10⁻²⁷) = 9.58 × 10⁷
C kg⁻¹
2. What are the quark compositions of a proton and a
neutron?
Answer:
Proton = uud (up, up, down)
Neutron = udd (up, down, down)
3. Explain why beta-plus decay cannot occur in free
protons.
Answer:
Beta-plus decay: p → n + e⁺ + νₑ
The proton mass (1.6726 × 10⁻²⁷ kg) is less than neutron
mass (1.6749 × 10⁻²⁷ kg), so free proton decay violates
conservation of mass-energy. It only occurs inside nuclei
where nuclear binding energy makes the process possible.
,4. Calculate the de Broglie wavelength of an electron
accelerated through 100 V.
Answer:
λ = h/√(2meV)
λ = (6.63 × 10⁻³⁴)/√(2 × 9.11 × 10⁻³¹ × 1.60 × 10⁻¹⁹ × 100)
λ = 1.23 × 10⁻¹⁰ m (0.123 nm)
Section 2: Waves
5. Explain the difference between progressive and
stationary waves.
Answer:
Progressive waves transfer energy; stationary waves store
energy. Progressive waves have all points oscillating with
same amplitude; stationary waves have nodes and
antinodes. Progressive waves have constant phase
difference between points; stationary waves have points
between nodes oscillating in phase.
6. Two waves interfere with path difference of 2.5λ.
What is the resulting interference?
Answer:
Path difference = nλ gives constructive interference (n
integer)
Path difference = (n+½)λ gives destructive interference
2.5λ = (2 + 0.5)λ → Destructive interference
,7. A diffraction grating has 500 lines/mm. Calculate
the grating spacing.
Answer:
d = 1/(500 × 10³) = 2.00 × 10⁻⁶ m (2000 nm)
8. Why does refraction occur when light passes
between media?
Answer:
Due to change in wave speed. The frequency remains
constant, but wavelength changes according to v = fλ. This
causes the wavefronts to change direction at the boundary
(Snell's Law: n₁sinθ₁ = n₂sinθ₂).
Section 3: Mechanics and Materials
9. State the principle of conservation of linear
momentum.
Answer:
In a closed system with no external forces, the total
momentum before collision equals total momentum after
collision.
10. A 2 kg ball moving at 3 m/s collides with a
stationary 1 kg ball. If they stick together, calculate
their final velocity.
Answer:
, Using conservation of momentum:
(2 × 3) + (1 × 0) = (2 + 1) × v
6 = 3v
v = 2 m/s
11. Define Young's modulus and give its units.
Answer:
Young's modulus = stress/strain
Units: Pa (Pascals) or N m⁻²
12. A wire of length 2.0 m extends by 0.5 mm under a
load of 200 N. Its diameter is 0.5 mm. Calculate
Young's modulus.
Answer:
Cross-sectional area A = π(0.25 × 10⁻³)² = 1.96 × 10⁻⁷ m²
Stress = F/A = 200/(1.96 × 10⁻⁷) = 1.02 × 10⁹ Pa
Strain = ΔL/L = (0.5 × 10⁻³)/2.0 = 2.5 × 10⁻⁴
Young's modulus = stress/strain = (1.02 × 10⁹)/(2.5 × 10⁻⁴)
= 4.08 × 10¹² Pa
Section 4: Electricity
13. State Ohm's Law and the conditions required for it
to be valid.
Answer:
Ohm's Law: V = IR, where V is potential difference, I is
SCHEME
Exam
Section 1: Particles and Radiation
1. Define specific charge and calculate it for a proton.
Answer:
Specific charge = charge/mass
For proton: charge = +1.60 × 10⁻¹⁹ C, mass = 1.67 × 10⁻²⁷
kg
Specific charge = (1.60 × 10⁻¹⁹)/(1.67 × 10⁻²⁷) = 9.58 × 10⁷
C kg⁻¹
2. What are the quark compositions of a proton and a
neutron?
Answer:
Proton = uud (up, up, down)
Neutron = udd (up, down, down)
3. Explain why beta-plus decay cannot occur in free
protons.
Answer:
Beta-plus decay: p → n + e⁺ + νₑ
The proton mass (1.6726 × 10⁻²⁷ kg) is less than neutron
mass (1.6749 × 10⁻²⁷ kg), so free proton decay violates
conservation of mass-energy. It only occurs inside nuclei
where nuclear binding energy makes the process possible.
,4. Calculate the de Broglie wavelength of an electron
accelerated through 100 V.
Answer:
λ = h/√(2meV)
λ = (6.63 × 10⁻³⁴)/√(2 × 9.11 × 10⁻³¹ × 1.60 × 10⁻¹⁹ × 100)
λ = 1.23 × 10⁻¹⁰ m (0.123 nm)
Section 2: Waves
5. Explain the difference between progressive and
stationary waves.
Answer:
Progressive waves transfer energy; stationary waves store
energy. Progressive waves have all points oscillating with
same amplitude; stationary waves have nodes and
antinodes. Progressive waves have constant phase
difference between points; stationary waves have points
between nodes oscillating in phase.
6. Two waves interfere with path difference of 2.5λ.
What is the resulting interference?
Answer:
Path difference = nλ gives constructive interference (n
integer)
Path difference = (n+½)λ gives destructive interference
2.5λ = (2 + 0.5)λ → Destructive interference
,7. A diffraction grating has 500 lines/mm. Calculate
the grating spacing.
Answer:
d = 1/(500 × 10³) = 2.00 × 10⁻⁶ m (2000 nm)
8. Why does refraction occur when light passes
between media?
Answer:
Due to change in wave speed. The frequency remains
constant, but wavelength changes according to v = fλ. This
causes the wavefronts to change direction at the boundary
(Snell's Law: n₁sinθ₁ = n₂sinθ₂).
Section 3: Mechanics and Materials
9. State the principle of conservation of linear
momentum.
Answer:
In a closed system with no external forces, the total
momentum before collision equals total momentum after
collision.
10. A 2 kg ball moving at 3 m/s collides with a
stationary 1 kg ball. If they stick together, calculate
their final velocity.
Answer:
, Using conservation of momentum:
(2 × 3) + (1 × 0) = (2 + 1) × v
6 = 3v
v = 2 m/s
11. Define Young's modulus and give its units.
Answer:
Young's modulus = stress/strain
Units: Pa (Pascals) or N m⁻²
12. A wire of length 2.0 m extends by 0.5 mm under a
load of 200 N. Its diameter is 0.5 mm. Calculate
Young's modulus.
Answer:
Cross-sectional area A = π(0.25 × 10⁻³)² = 1.96 × 10⁻⁷ m²
Stress = F/A = 200/(1.96 × 10⁻⁷) = 1.02 × 10⁹ Pa
Strain = ΔL/L = (0.5 × 10⁻³)/2.0 = 2.5 × 10⁻⁴
Young's modulus = stress/strain = (1.02 × 10⁹)/(2.5 × 10⁻⁴)
= 4.08 × 10¹² Pa
Section 4: Electricity
13. State Ohm's Law and the conditions required for it
to be valid.
Answer:
Ohm's Law: V = IR, where V is potential difference, I is
