A-Level H2 Physics 4 — Questions and Answers
Question 1: What is the first law of thermodynamics?
- Energy cannot be created or destroyed in an isolated system
- ΔU = Q + W, where ΔU is change in internal energy, Q is heat added, and W is work done on the system (Correct answer)
- Entropy always increases
- Heat flows from cold to hot
Correct answer: ΔU = Q + W, where ΔU is change in internal energy, Q is heat added, and W is work done on the system
First law of thermodynamics: ΔU = Q + W. The change in internal energy equals heat added to the system plus work done on the system. It is the law of conservation of energy for thermodynamic systems.
Question 2: What is the condition for stationary waves to form?
- Two waves of the same frequency and amplitude travelling in the same direction
- Two coherent waves of the same frequency and amplitude travelling in opposite directions (Correct answer)
- Any two waves meeting at a point
- Waves reflecting off a soft boundary only
Correct answer: Two coherent waves of the same frequency and amplitude travelling in opposite directions
Stationary (standing) waves form when two waves of the same frequency, amplitude, and wavelength travel in opposite directions and superpose. They have fixed nodes and antinodes.
Question 3: A proton is accelerated from rest through a potential difference of 500V. What kinetic energy does it gain? (e = 1.6×10⁻¹⁹ C)
- 8×10⁻¹⁷ J (Correct answer)
- 3.2×10⁻¹⁶ J
- 1.6×10⁻¹⁶ J
- 5×10⁻¹⁸ J
Correct answer: 8×10⁻¹⁷ J
KE gained = qV = 1.6×10⁻¹⁹ × 500 = 8×10⁻¹⁷ J.
Question 4: What is the difference between progressive and stationary waves?
- Progressive waves transfer energy; stationary waves do not transfer energy in the direction of the wave (Correct answer)
- They are the same
- Stationary waves have higher frequency
- Progressive waves have nodes
Correct answer: Progressive waves transfer energy; stationary waves do not transfer energy in the direction of the wave
Progressive waves transfer energy from one point to another. Stationary waves have nodes and antinodes — energy is stored between nodes but not transferred in the direction of the wave.
Question 5: What is the formula for gravitational field strength?
- g = GMr
- g = GM/r² (Correct answer)
- g = Gm/r
- g = GM/r
Correct answer: g = GM/r²
Gravitational field strength g = GM/r², where G is the gravitational constant, M is the mass of the body causing the field, and r is the distance from its centre.
Question 6: What is meant by 'isotopes'?
- Atoms of different elements with the same mass number
- Atoms of the same element with the same number of protons but different numbers of neutrons (Correct answer)
- Atoms with the same number of electrons
- Atoms with the same number of neutrons
Correct answer: Atoms of the same element with the same number of protons but different numbers of neutrons
Isotopes are atoms of the same element (same atomic number/protons) but with different numbers of neutrons, and therefore different mass numbers.
A-Level H2 Physics 4
What is the first law of thermodynamics?