Uses and hazards of electromagnetic waves

Fluorescent tube lamps can be used in schools and office buildings for lighting.

The photograph shows an engineer installing a fluorescent tube lamp.

Diagram 1 shows a simplified view of the components of a fluorescent tube lamp.

When the lamp is on, a large voltage is applied between the positive electrode and the negative electrode.

State what is meant by the term voltage.

The large voltage causes electrons to accelerate from the negative electrode towards the positive electrode.

An electron gains 1.0 × 10^–16J of energy when it accelerates between the electrodes.

Show that the voltage between the electrodes is about 600 V.

[magnitude of electron charge = 1.6 × 10^–19C]

The electron gains 1.0 × 10^–16J of energy in its kinetic store when it accelerates from the negative electrode to the positive electrode.

Calculate the speed of an electron when it reaches the positive electrode.

Assume the electron is initially at rest.

[electron mass = 9.1 × 10^–31kg]

When the electrons accelerate between the electrodes, they collide with mercury atoms.

Energy is transferred to the mercury atoms during the collisions. This causes the mercury atoms to emit ultraviolet light.

Atoms in the fluorescent coating absorb this ultraviolet light, which is then re‑emitted as light from a different part of the electromagnetic spectrum.

Diagram 2 shows this process.

Suggest why the tube must have a fluorescent coating for the lamp to operate effectively.

Explain why the fluorescent tube lamp is dangerous if the fluorescent coating becomes damaged.

The table shows an incomplete electromagnetic spectrum.

Two parts of the electromagnetic spectrum are missing.

The missing parts are labelled A and B.

Name the part labelled A.

Name the part labelled B.

Give a use of microwaves.

Give a use of gamma rays.

The photograph shows infrared heating lamps being used to harden fresh paint on

Give a harmful effect of infrared waves.

The heating lamps produce visible light waves in addition to infrared waves.

Give two similar properties of visible light waves and infrared waves.

Give two differences between the properties of visible light waves and infrared waves.

The infrared heating lamps are placed 1.5 m from the car.

Calculate the time taken for infrared waves emitted from a lamp to reach the car.

[for infrared waves, speed = 3.0 × 10⁸m/s]

Paint takes less time to harden when it absorbs more energy from infrared radiation.

A technician observes that white paint takes more time to harden than black paint.

Explain this observation.

This question is about microwave ovens and microwaves.

A microwave oven cooks some food.

Diagram 1 represents a microwave emitted by the microwave oven.

Determine the wavelength of the microwave.

The microwave has a frequency of 2.35 GHz.

Show that the speed of the microwave is about 310⁸m/s.

Diagram 2 shows a damaged microwave oven with a hole in the door.

This microwave oven should not be used as it is very dangerous.

State a harmful effect from the microwaves if this oven is used.

This question is about the electromagnetic spectrum.

The table gives some statements about the electromagnetic spectrum.

Place three ticks () in the table to show which statements are correct.

Electromagnetic waves can be useful, but can also be harmful.

Give one use and one harmful effect of microwaves.

use

harmful effect

Give one use and one harmful effect of gamma rays.

use

harmful effect

Ground-penetrating radar (GPR) uses radio waves to detect changes in material underground.

State the formula linking the speed, frequency and wavelength of a wave.

GPR radio waves have a frequency of 170 MHz.

The speed of radio waves is 3.0 × 10⁸m / s.

Calculate the wavelength of the waves.

A radio wave passes through the ground and refracts at the boundary between soil and rock.

The diagram shows three wavefronts of the wave before and after refraction.

The wave is also reflected at the boundary between the soil and the rock.

Complete the diagram to show three wavefronts after the wave has been reflected at the boundary.

Explain why the radio waves passing through the rock have a smaller wavelength than the radio waves passing through the soil.

The photograph shows an x-ray image of a person’s knee. The person has had part of their knee replaced.

X-rays are part of the electromagnetic spectrum.

All electromagnetic waves are transverse waves and transfer energy.

State another property that all electromagnetic waves have in common.

State a harmful effect of excessive exposure to x-rays.

Describe the difference between transverse waves and longitudinal waves.

You may draw a diagram to help your answer.

The diagram shows a part of the knee called the patella. The patella has been removed from a person’s knee.

The patella is a small, irregularly shaped bone that is denser than water.

Describe how to find the mass and the volume of the patella bone.

A scientist finds the volume and mass of a patella.

The mass of the patella is 17 g.

The volume of the patella is 13 cm³.

Calculate the density of the patella.

Give your answer to 2 significant figures.

density =_........ g / cm³

This is a question about electromagnetic waves.

State which colour in the visible spectrum has the shortest wavelength.

Explain a hazard of ultraviolet radiation to the human body.

State the formula linking speed, wavelength and frequency of a wave.

Calculate the frequency of radio waves with a wavelength of 15 m.

[speed of light = 300 000 000 m/s]

This question is about electromagnetic waves.

Draw a straight line from each electromagnetic wave to its correct use.

One has been done for you.

Electromagnetic wave
Use

State a hazard to humans of excessive exposure to infrared waves.

State a precaution that would reduce a person’s risk of exposure to ultraviolet waves.

X‑rays and gamma rays are examples of ionising radiation.

Which of these is another example of ionising radiation?

Give one use of x‑rays and one use of gamma rays.

x‑rays

gamma rays

State the formula linking speed, frequency and wavelength of a wave.

Calculate the wavelength of a gamma ray with a frequency of 2.8 × 10¹⁹Hz.

[speed of gamma ray = 3.0 × 10⁸m/s]

X‑rays and gamma rays are electromagnetic waves.

Which of these graphs is correct for waves travelling at a constant speed?

The photograph shows a security camera.

The camera detects light waves and sound waves.

State two differences between light waves and sound waves.

The camera detects infrared waves, which allow the camera to record videos in the dark.

Which of these electromagnetic waves has a longer wavelength than infrared waves?

Which of these is another use for infrared waves?

Which of these is a harmful effect of infrared waves?

The grid shows the oscilloscope trace for a quiet, low‑pitch sound wave.

The security camera has an alarm that produces a loud, high‑pitch sound.

On the grid, draw a trace to represent the sound wave produced by the alarm.

This question is about electromagnetic (EM) waves.

The boxes show some EM waves and their uses.

Draw one straight line from each EM wave to its correct use.

One has been done for you.

EM wave
Use

Which of these is a hazard of microwave radiation?

State the name of an electromagnetic wave with a wavelength longer than microwave radiation.