OCR A-Level Physics A H556
Practical Skills in the Written Papers
The Practical Endorsement
Physical Quantities and Units
Making Measurements and Analysing Data
Nature of Quantities
Motion
Forces in Action
Work, Energy and Power
Materials
Newton’s Laws of Motion and Momentum
Charge and Current
Energy, Power and Resistance
Electrical Circuits
Waves
Quantum Physics
Thermal Physics
Oscillations
Gravitational Fields
Astrophysics and Cosmology
Capacitors
Electric Fields
Electromagnetism
Nuclear and Particle Physics
Quantum Physics
Photons, electronvolts and the Planck constant from LEDs
- 3 things to know
- Papers 2 and 3
Overview
Recall questions on the photon model, photon energy in terms of frequency and wavelength, the electronvolt, and estimating the Planck constant from the threshold voltages of LEDs.
What you need to know
Answer each one before you reveal it.
What does the photon model describe about the nature of electromagnetic radiation?
Define a photon.
Questions from this subtopic
Each one with the model answer underneath.
- 1
What does the photon model describe about the nature of electromagnetic radiation?
Model answer
Electromagnetic radiation has a particulate nature, consisting of discrete packets of energy called photons.
- 2
Define a photon.
Model answer
A photon is a quantum of energy of electromagnetic radiation, representing the smallest indivisible unit of light energy.
- 3
Calculate the photon energy when Planck constant = 6.63 × 10⁻³⁴ J s, frequency = 6.22 × 10¹⁴ Hz.
Model answer
Photon energy = 6.63 × 10⁻³⁴ × 6.22 × 10¹⁴ = 4.12 × 10⁻¹⁹ J.
- 4
State the alternative equation for photon energy in terms of wavelength.
Model answer
E = hc/λ, where h is the Planck constant, c is the speed of light, and λ is the wavelength.
- 5
Calculate the photon energy when Planck constant = 6.63 × 10⁻³⁴ J s, speed of light = 3.00 × 10⁸ m s⁻¹, wavelength = 4.50 × 10⁻⁷ m.
Model answer
Photon energy = (6.63 × 10⁻³⁴ × 3.00 × 10⁸) ÷ (4.50 × 10⁻⁷) = 4.42 × 10⁻¹⁹ J.
- 6
Define the electronvolt.
Model answer
The electronvolt is a unit of energy equal to the energy gained by an electron when accelerated through a potential difference of one volt.
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