Chapter 7 Rays and waves Flashcards
What are luminous objects?
Objects which emit their own light
What are examples of luminous objects?
The Sun, lamps, lasers and glowing TV screens
What is a non-luminous object?
An object which does not emit its own light
How can we see non-luminous objects?
Non-luminous objects reflect light and some of it goes into our eyes
Why do white objects look white?
They reflect most light and therefore look white
Why do black objects look black?
They absorb nearly all the light striking them and reflect very little, therefore they look black
What is diffuse reflection?
When a surface reflects light rays in all directions
What might cause diffuse reflection?
A surface might be uneven or contain particles which scatter light
What is regular reflection?
When a surface reflects light rays at the same angle of reflection
What might cause regular reflection?
A surface might be smooth
What happens when a material transmits light?
The material lets light pass through it
What are the important features of light?
Light is a form of radiation, travels in straight lines, transfers energy, travels as waves, can travel through empty space and is the fastest thing there is
What does light being a form of radiation mean?
Light radiates (spreads out) from its source
How does light transfer energy?
Energy is needed to produce light and materials gain energy when they absorb light
How can some effects of light be best explained?
Some effects can best be explained by thinking of light as a stream of tiny “energy particles”
What are photons?
Particles thought to be tiny “energy particles” which can form a stream which is light
Does light need a medium to travel through?
No
What is the speed of light? (approximate)
300,000 kilometres per second
What is the speed of light? (exact)
299,792,458 m/s
Can anything travel faster than light?
No
Do light waves have low or high frequencies?
Light waves have extremely high frequencies
What causes us to see different colours?
The brain senses different wavelengths as different colours
What is the wavelength of violet light?
0.0004 mm
What is the wavelength of red light?
0.0007 mm
Do most sources emit monochromatic light or a mixture of wavelengths?
Most sources emit a mixture of wavelengths
What is monochromatic light?
Light of a single wavelength
What type of light do lasers emit?
Monochromatic light
In reflection, what is the incident ray?
The incoming ray that strikes the reflective surface
In reflection, what is the reflected ray?
The outgoing ray, reflected from the reflective surface
What is the normal in reflection?
The line at right angles to the reflective surface a ray strikes
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
What is the law of reflection regarding angle sizes?
The angle of incidence is equal to the angle of reflection
What is the law of reflection regarding planes?
The incident ray, reflected ray and the normal all lie in the same plane
What is a plane mirror?
A flat mirror
When rays from an object reflect from a mirror and enter a person’s eyes, what is the image?
A copy of the object which appears to exist behind the mirror
What is the one important difference between an image in a mirror and the actual object?
The image is laterally inverted (back to front)
What type of image is the one in a plane mirror?
A virtual image
Why is the image in a plane mirror a virtual one?
No rays actually pass through the image and it can’t be formed on a screen
How large is an image formed by a plane mirror?
The image is the same size as the object
Where is the image formed by a plane mirror?
The image is as far behind the mirror as the object is in front
How would a line joining equivalent points on an object and its image formed by a plane mirror intersect the plane mirror?
It would pass through the mirror at right angles
What is the more complicated method of finding the position of an image in a plane mirror?
Draw two rays from the actual object which strike and are reflected from the mirror and extend the reflected rays until they intersect at a point, I, which is the image position
What is the simpler method of finding the position of an image in a plane mirror?
From the object, draw a line which intersects the mirror at right angles, extend it well into the mirror and mark the point, I, as far behind the mirror as the object is in front, which is the image position
What is refraction in terms of light?
The bending of a light ray when it passes from one medium to another
If a ray passes through a transparent block with parallel sides, how would the original direction and the direction of the emerging ray compare?
The ray would emerge parallel to its original direction
What is the refracted ray?
The ray in the new medium which travels in a different direction to the incident ray
What is the angle of refraction?
The angle between the refracted ray and the normal
In what direction does light refract when passing from a less dense to a more dense medium?
Light is refracted towards the normal
In what direction does light refract when passing from a more dense to a less dense medium?
Light is refracted away from the normal
What is real and apparent depth in water?
Real depth is the true depth of an object in water whilst apparent depth is how deep it appears to be in the water
What causes refraction in light?
When a light beam passes from one medium into another, one side of the beam changes speed before the other, causing the beam to “bend”.
What is the formula for the refractive index of a medium?
refractive index = speed of light in vacuum / speed of light in medium
What is the refractive index of diamond?
2.42
What is the refractive index of glass (crown)?
1.52
What is the refractive index of acrylic plastic (Perspex)?
1.49
What is the refractive index of water?
1.33
