The Electromagnetic Spectrum: Physics 0625 (Cambridge O Level / IGCSE)

Which list correctly places four regions of the electromagnetic spectrum in order of increasing wavelength (shortest wavelength first)?

(a) State how the speed of X-rays through a vacuum compares with the speed of radio waves through a vacuum. [1]

(b) State one everyday use of microwaves. [1]

(c) State one everyday use of infrared radiation. [1]

(d) State one harmful effect on living cells caused by exposure to ultraviolet radiation. [1]

(a) State the equation linking the speed, frequency and wavelength of a wave. [1]

(b) A wireless router transmits a wireless internet signal of frequency $2400\text{ MHz}$ through air, in which electromagnetic waves travel at a speed of $3.0\times10^{8}\text{ m/s}$. Calculate the wavelength of this signal. Give your answer in metres, to 2 significant figures. [2]

(c) State which region of the electromagnetic spectrum this wavelength belongs to. [1]

A WiFi router uses microwaves to send an internet signal to a laptop in a different room, through a closed door. The same laptop also has an infrared port, once used to transfer files directly to another device, but this only worked when the two devices were placed facing each other with a clear, unobstructed view between them. Which statement best explains why microwaves, rather than infrared radiation, are used to carry the WiFi signal to a device in another room?

A mobile-phone signal has frequency $1800\text{ MHz}$. An FM radio broadcast has wavelength $3.2\text{ m}$. Both signals travel through air at $3.0\times10^{8}\text{ m/s}$.

(a) Calculate the wavelength of the mobile-phone signal. Give your answer in metres, to 2 significant figures. [2]

(b) Calculate the frequency of the FM radio signal. Give your answer in standard form, to 2 significant figures. [2]

(c) State which of the two signals, the mobile-phone signal or the FM radio signal, has the higher frequency and the shorter wavelength. [1]

(d) Both signals lie towards the low-frequency end of the electromagnetic spectrum, where the radiation is non-ionising. Explain why exposure to radio waves and microwaves at typical everyday intensities is not considered as harmful as exposure to ultraviolet or X-ray radiation. [2]

A wave travels through a vacuum with a wavelength of $5.0\times10^{-7}\text{ m}$ (500 nm). Which region of the electromagnetic spectrum does this wave belong to?

A UV germicidal lamp in a water-purification plant emits ultraviolet radiation of wavelength $254\text{ nm}$ ($2.54\times10^{-7}\text{ m}$) in air, where electromagnetic waves travel at $3.0\times10^{8}\text{ m/s}$.

(a) Calculate the frequency of this ultraviolet radiation. Give your answer in standard form, to 3 significant figures. [2]

(b) State one everyday use of ultraviolet radiation, other than purifying water. [1]

(c) Visible red light has a longer wavelength than this ultraviolet radiation, at about $700\text{ nm}$. State how the frequency of red light compares with the frequency of the ultraviolet radiation found in part (a), and explain your answer using the wave speed equation. [2]

A satellite television company sends a signal from a ground transmitter, up through the ionosphere (a charged layer of Earth's atmosphere), to a satellite in orbit, which then sends the signal back down through the ionosphere to a receiver dish elsewhere on Earth's surface. The company uses microwaves for this link, rather than radio waves of much lower frequency. Which statement best explains this choice?

Doctors in a hospital use two different regions of the electromagnetic spectrum: X-rays to image a patient's broken bone, and gamma rays to treat a cancerous tumour.

(a) State why both X-rays and gamma rays must be used carefully, in terms of their effect on living cells. [1]

(b) A radiographer who takes X-ray photographs every day stands behind a lead screen, or leaves the room, while each X-ray is taken. Explain why this precaution is necessary. [2]

(c) Suggest one everyday, non-medical use of X-rays. [1]

A laser pointer emits green light of wavelength $532\text{ nm}$ in air, where electromagnetic waves travel at $3.0\times10^{8}\text{ m/s}$. A nearby radio transmitter broadcasts at a frequency of $1.5\times10^{6}\text{ Hz}$.

(a) Convert the wavelength of the green light into metres, giving your answer in standard form. [1]

(b) Calculate the frequency of the green light. Give your answer in standard form, to 3 significant figures. [2]

(c) Calculate how many times greater the frequency of the green light is than the frequency of the radio wave. Give your answer to 2 significant figures. [2]

(d) State which of the two waves, the green light or the radio wave, carries more energy, and explain your answer in terms of frequency. [2]