Energy and momentum of a photon

State the meaning of a photon.

Feb/March 2025

A $\pi^{0}$ meson is a sub-atomic particle. When a $\pi^{0}$ meson is at rest, and has mass $2.4 \times 10^{-28}\,\text{kg}$, it decays to produce two $\gamma$-ray photons. The nuclear equation representing this decay is $\pi^{0} \rightarrow \gamma + \gamma$.

May/June 2010

In an optic fibre, the signal-to-noise ratio must stay at or above $24\,\text{dB}$. The mean noise power in the fibre is $5.6\times10^{-19}\,\text{W}$. Calculate the minimum effective signal power in the optic fibre.

May/June 2011

In an optic fibre, the signal-to-noise ratio must stay above $24\,\text{dB}$. The mean noise power in the fibre is $5.6 \times 10^{-19}\,\text{W}$. Calculate the minimum effective signal power in the optic fibre.

May/June 2011

High-speed electrons strike a metal target. Figure 11.1 shows the spectrum of the emitted X-ray radiation.

May/June 2012

A beam of light of wavelength $590\,\text{nm}$ falls normally on a surface, as shown in Fig. 8.1. Its power is $3.2\,\text{mW}$. The surface absorbs all of the light.

May/June 2014

In magnetic resonance imaging, which is used to gather details about structures inside the body, a large constant magnetic field is applied together with a calibrated magnetic field that is non-uniform.

May/June 2015

A photon with wavelength $6.50 \times 10^{-12}\,\text{m}$ strikes an isolated electron that is initially at rest, as shown in Fig. 8.1. The electron of mass $m_e$ scatters the photon elastically. After deflection, the photon has wavelength $6.84 \times 10^{-12}\,\text{m}$.

May/June 2015

Explain what the term photon means.

May/June 2015

In magnetic resonance imaging, which is used to gather information about internal body structures, a large constant magnetic field is applied and a calibrated non-uniform magnetic field is superimposed on top of it.

May/June 2015

A photon with wavelength $6.50 \times 10^{-12}\,\text{m}$ strikes an isolated electron that is initially at rest, as shown in Fig. 8.1. The photon is elastically deflected by the electron of mass $m_e$. The wavelength of the photon after deflection is $6.84 \times 10^{-12}\,\text{m}$.

May/June 2015

State what a photon is.

May/June 2019

An electron, while stationary, has mass $m_e$ and charge $-q$. A positron is a particle that, when at rest, has mass $m_e$ and charge $+q$. A positron then interacts with an electron. The electron and the positron can be treated as being at rest. The result of this interaction is that the electron and the positron turn into two gamma-ray ($\gamma$-ray) photons, each with the same energy.

May/June 2020

An electron has rest mass $m_e$ and charge $-q$. A positron is a particle with rest mass $m_e$ and charge $+q$ when at rest. An electron and a positron interact. They may be treated as stationary. As a result, the electron and positron are converted into two gamma-ray ($\gamma$-ray) photons, each with the same energy.

May/June 2020

State what the term photon means.

May/June 2021

State what the term photon means.

May/June 2024

State what the term photon means.

May/June 2024

Cable television relies on optic fibres to carry signals. Suggest four benefits of optic fibres compared with coaxial cables for data transmission.

Oct/Nov 2011

State the meaning of the term photon.

Oct/Nov 2014

State the meaning of the term photon.

Oct/Nov 2017

State the meaning of a photon.

Oct/Nov 2017

An isolated nucleus, initially at rest, emits a $\gamma$-ray photon with energy $0.51\,\text{MeV}$.

Oct/Nov 2018

An isolated nucleus that is initially at rest emits a $\gamma$-ray photon with energy $0.51\,\text{MeV}$.

Oct/Nov 2018

A photon with wavelength $540\,\text{nm}$ strikes an isolated stationary electron, as shown in Fig. 11.1. The electron causes the photon to be elastically deflected. The wavelength of the scattered photon is $544\,\text{nm}$.

Oct/Nov 2020

As shown in Fig. 11.1, a photon with wavelength $540\,\text{nm}$ strikes an isolated electron that is initially at rest. The electron deflects the photon elastically. The wavelength of the scattered photon is $544\,\text{nm}$.

Oct/Nov 2020

Show that a photon of electromagnetic radiation with wavelength $\lambda$ has momentum $p = \frac{h}{\lambda}$, where $h$ is the Planck constant.

Oct/Nov 2023

Show that the momentum $p$ of a photon of electromagnetic radiation with wavelength $\lambda$ is $p = \frac{h}{\lambda}$, where $h$ is the Planck constant.

Oct/Nov 2023