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GCSE Physics

GCSE Physics Flash Card Questions

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P14 Light

P14.1 Reflection of light (single science only)

Question	Answer
What is a plane mirror?	a perfectly flat mirror
What is the normal on a mirror?	a line drawn perpendicular to the mirror at a point on the mirror
What is reflection?	when light strikes a surface and then travels away from the barrier, it is said to have been reflected
What is the incident ray in reflection?	the ray that travels towards and strikes the surface
What is the reflected ray in reflection?	the ray that travels away from the surface after striking it
Compare the frequency of the incident and reflected rays.	the incident and reflected rays have the same frequency
Compare the speed of the incident and reflected rays.	the incident and reflected rays have the same speed
What is the angle of incidence?	the angle between the incident ray and the normal
What is the angle of reflection?	the angle between the reflected ray and the normal
State the law of reflection.	the angle of incidence = the angle of reflection
How is a point image formed in a mirror?	• the light strikes the mirror • the light is reflected off the mirror obeying the law of reflection • the light reaches the eye and the signal sent to the brain • the brain assumes that the light travelled in a straight line from object to eye • the brain extends the rays of light to behind the mirror until they intersect
Compare the properties of the object and the image formed in a plane mirror.	• the image and object are the same size • the image and object are the same distance from the mirror. • the image and object are the same way up • the object is back-to-front compare the image (lateral inversion) • the image is virtual
What is a virtual image?	a virtual image is formed at a place where light rays appear to come from after they have been reflected or refracted
What is a real image?	a real image is formed by focusing light rays onto a screen
State an example of a virtual image.	the image in a mirror
State an example of a real image.	the image on the screen at the cinema
Why is it possible to see a clear image in a mirror?	a mirror has a smooth surface that reflects rays without scattering them
What is reflection called from a smooth surface?	specular reflection because parallel light rays are reflected in a single direction
What is reflection called from a rough surface?	diffuse reflection because the light is scattered in different directions

P14 Light

P14.2 Refraction of light (single science only)

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Question	Answer
What is refraction?	the bending of light when it passes from one medium to another
Name two types of waves that are refracted.	light and sound
When does refraction happen with water waves?	when water waves move from deep to shallow water at a non-zero angle
What happens to a wave when it is refracted?	the wave changes speed and therefore direction
Why is light refracted between air and glass?	light travels more slowly in glass than air
Considering light moving from air into glass and out again, how is light refracted?	• from air into glass, light bends towards the normal • from glass into air, light bends away from the normal
Which is more optically dense, glass or air?	light moves more slowly in glass than air, so glass is more optically dense
State the general rule for refraction for light.	• light bends towards the normal when moving from a less to more dense medium • light bends away from the normal when moving from a more to a less dense medium
Why do you see a faint reflection of yourself when looking through a mirror?	because part of the light is reflected and part diffracted
Is the refracted ray as strong as the incident ray?	when waves cross a boundary between two materials, partial reflection can happen as well as refraction in which the refracted ray will be weaker than the incident ray
What is partial refraction?	when the incident ray light is not fully refracted but some is reflected
Why do refracted rays have a smaller amplitude than the incident ray?	the refracted rays lose energy at the boundary
State the refraction rules for angles.	• when light passes from a less to a more dense medium, the incident angle is greater than the refracted angle • when light passes from a more to a less dense medium, the incident angle is less than the refracted angle

P14 Light

P14.3 Light and colour (single science only)

Question	Answer
What defines a colour of light?	the frequency (or wavelength) of the light
Do all light sources emit the same wavelengths of light?	no, each light source emits its own range of wavelengths
Name two light sources that emit a broad spectrum of light.	• stars like the sun emit light that has a continuous range of wavelengths across the visible spectrum • a filament lamp is also a white light source
Name two light sources that emit a narrow range of wavelengths	• lasers • neon lamps • a sodium light emits a yellow/orange light
How does a colour filter work?	it absorbs certain wavelengths and transmits other wavelengths
What happens if white light is directed at a red filter?	red light will be transmitted and all other wavelengths of light will be absorbed
What are the primary colours of light?	red, blue, and green
Why are red, blue and green referred to as the primary colours of light?	because they can be mixed to produce any other colour of light
What does opaque mean?	not able to be seen through; not transparent
What does the colour of an opaque surface depend on?	the chemicals called pigments in the surface
Aside from surface pigments, what does the colour of an object depend on?	the range of wavelenghts in the incident light
Why does a white surface look white in daylight?	daylight contains all wavelengths and the surface reflects all wavelengths
Why does the same white surface look different indoors?	the surface still reflects all wavelengths but because indoor light bulbs do not contain the same spectrum of wavelengths as natural light, the surface will appear a different colour
What gives pigments specific colours?	pigments absorb light of specific wavelenths, and strongly reflect other wavelengths
Why does a white surface reflect light of any wavelength?	a white surface has no pigments
What makes a book with a red cover look red in daylight?	the cover reflects the red light in daylight and absorbs all other colours
What colour would a book with a red cover look under a blue light?	the cover of the book would look black as it absorbs the blue light and there is no red light to reflect
What does transparent mean?	allowing light to pass through so that objects behind can be distinctly seen
Why is a window transparent?	because the window neither reflects nor absorbs any wavelengths so an object can be seen clearly through the window
What does translucent mean?	allowing light, but not detailed shapes, to pass through; semi-transparent
Why can one not see through a translucent medium when light passes through?	the light is scattered and refracted as it passes through the surface
Why is light scattered and refracted through a translucent medium?	because the material of the medium has plenty of internal boundaries in it
Why makes an object opaque?	the light is either reflected, scattered, or absorbed on the surface - no light travels all the way through the object

P14 Light

P14.4 Lenses (single science only)

Question	Answer
Name a device that uses lenses.	a camera
What does a lens do?	a lens works by changing the direction of light passing through it
How does a convex lens affect parallel rays of light?	it makes parallel rays converge to a point called a focus
Sketch a diagram of parallel rays of light passing through a convex lens.
What is another name for a convex lens?	a converging lens
State a practical example of a convex lens being used.	• a magnifying glass to enlarge an image • a camera to form a clear image of a distant object
How does a concave lens affect parallel rays?	it makes parallel rays diverge such that the rays appear to be coming from a point on the same side of the lens as the parallel rays
Sketch a diagram of parallel rays of light passing through a concave lens.
What is another name for a concave lens?	a diverging lens
State a practical use of a concave lens.	a concave lens is used to correct short sight
What is the focal length?	the distance from the centre of the lens to the principal focus
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P14 Light

P14.5 Using lenses (single science only)

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