Light and the EM Spectrum

What is the law of reflection?

The angle of incidence equals the angle of reflection. Both angles are measured from the normal.

What is reflection?

Reflection is when a wave or ray bounces off a surface and remains in the original medium.

What is refraction?

Refraction is the change in direction of light as it passes between different media because its speed changes.

What is total internal reflection (TIR)?

TIR occurs when light travelling in a more optically dense medium reaches a boundary with a less optically dense medium at an angle greater than the critical angle, causing all the light to be reflected back.

What is the critical angle?

The critical angle is the angle of incidence in the more optically dense medium that produces an angle of refraction of 90°.

What two conditions are required for total internal reflection?

Light must travel from a more optically dense medium to a less optically dense medium, and the angle of incidence must be greater than the critical angle.

What is specular reflection?

Specular reflection is reflection from a smooth surface where parallel incident rays remain parallel after reflection.

What is diffuse reflection?

Diffuse reflection occurs from a rough surface where reflected rays are scattered in different directions.

Why does an object appear a particular colour?

It appears that colour because some wavelengths of visible light are absorbed at its surface while the wavelengths corresponding to its colour are reflected into the observer's eyes.

How do filters produce coloured light?

A filter transmits certain wavelengths of light and absorbs other wavelengths.

What determines the power of a lens?

The power of a lens depends on its focal length. A shorter focal length means a more powerful lens.

What is the relationship between lens power and focal length?

Power = 1 ÷ focal length in metres. Power is measured in dioptres (D).

What does a converging lens do to parallel rays of light?

It refracts parallel rays so that they converge at the principal focus.

What does a diverging lens do to parallel rays of light?

It refracts parallel rays so that they diverge, appearing to come from a virtual focus.

What is a real image?

A real image is formed where light rays actually meet and can be projected onto a screen.

What is a virtual image?

A virtual image is formed where light rays appear to come from but do not actually meet, so it cannot be projected onto a screen.

How does a converging lens produce different types of images?

Depending on the object's distance from the lens, a converging lens can produce real or virtual images with different sizes and orientations.

How does a diverging lens form an image?

A diverging lens produces a virtual, upright and diminished image for a real object.

What is the core practical for Topic 5?

Investigate refraction in rectangular glass blocks in terms of the interaction of electromagnetic waves with matter.

What type of wave is every electromagnetic wave?

All electromagnetic waves are transverse waves.

What speed do all electromagnetic waves travel at in a vacuum?

All electromagnetic waves travel at approximately 3.0 × 10⁸ m/s in a vacuum.

What do electromagnetic waves transfer?

Electromagnetic waves transfer energy from a source to an observer.

What is the order of the electromagnetic spectrum from longest to shortest wavelength?

Radio waves → microwaves → infrared → visible light → ultraviolet → X-rays → gamma rays.

What is the order of the electromagnetic spectrum from lowest to highest frequency?

Radio waves → microwaves → infrared → visible light → ultraviolet → X-rays → gamma rays.

How does wavelength change across the electromagnetic spectrum from radio waves to gamma rays?

Wavelength decreases.

How does frequency change across the electromagnetic spectrum from radio waves to gamma rays?

Frequency increases.

Which colours make up visible light in order of increasing frequency?

Red → orange → yellow → green → blue → indigo → violet.

What range of electromagnetic radiation can human eyes detect?

Human eyes detect only a limited range of electromagnetic radiation called visible light.

Can different substances affect electromagnetic waves differently?

Yes. Different substances may absorb, transmit, refract or reflect electromagnetic waves differently depending on their wavelength.

Why can electromagnetic waves refract when entering a different substance?

Their velocity changes when they enter a different substance, which can cause their direction to change.

What determines the intensity and wavelength distribution of radiation emitted by a body?

The temperature of the body determines the intensity and wavelength distribution of its emitted radiation.

What condition is required for a body to remain at a constant temperature?

The average power it radiates must equal the average power it absorbs.

What happens if a body radiates less average power than it absorbs?

It gains energy and its temperature increases.

What happens if a body radiates more average power than it absorbs?

It loses energy and its temperature decreases.

What affects the temperature of the Earth?

The Earth's temperature depends on the balance between incoming radiation from the Sun and radiation emitted by the Earth.

What is investigated in the thermal radiation core practical?

How the nature of a surface affects the amount of thermal energy radiated or absorbed.

How does the potential danger of electromagnetic radiation change with frequency?

The potential danger generally increases as frequency increases because higher-frequency radiation carries more energy per photon.

What are the harmful effects of excessive microwave exposure?

Microwaves can cause internal heating of body cells.

What are the harmful effects of excessive infrared exposure?

Infrared can cause skin burns.

What are the harmful effects of excessive ultraviolet exposure?

Ultraviolet radiation can damage surface cells and eyes and can lead to skin cancer and eye conditions.

What are the harmful effects of excessive X-ray and gamma-ray exposure?

X-rays and gamma rays can cause mutations or damage cells in the body.

What are radio waves used for?

Radio waves are used for broadcasting, communications and satellite transmissions.

What are microwaves used for?

Microwaves are used for cooking, communications and satellite transmissions.

What is infrared used for?

Infrared is used for cooking, thermal imaging, short-range communications, optical fibres, television remote controls and security systems.

What is visible light used for?

Visible light is used for vision, photography and illumination.

What is ultraviolet radiation used for?

UV is used for security marking, fluorescent lamps, detecting forged bank notes and disinfecting water.

What are X-rays used for?

X-rays are used to observe the internal structure of objects, in airport security scanners and for medical imaging.

What are gamma rays used for?

Gamma rays are used to sterilise food and medical equipment and to detect and treat cancer.

How can radio waves be produced?

Radio waves can be produced by oscillations in electrical circuits.

What can radio waves do to electrical circuits?

Radio waves can induce oscillations in electrical circuits.

How can changes in atoms and nuclei generate electromagnetic radiation?

Changes in atoms and nuclei can generate electromagnetic radiation across a wide range of frequencies.

How can changes in atoms and nuclei be caused by electromagnetic radiation?

Atoms and nuclei can absorb electromagnetic radiation, causing changes within them.

What is the relationship between frequency and wavelength for electromagnetic waves?

For electromagnetic waves in a vacuum, c = f × λ. As frequency increases, wavelength decreases because their speed is constant.

What is the key idea behind the refraction practical with rectangular glass blocks?

Light changes direction and speed when passing between air and glass, allowing the relationship between the incident and refracted rays to be investigated.