Light

Question 1

Reflection of light

Answer 1

The bouncing of light off the surface of a body. If the surface is smooth, there will be regular reflection. If it is rough, the reflection will be diffuse.

Question 2

Mirror

Answer 2

A smooth polished surface, which is used for regular reflection of light

Question 3

The law of reflection

Answer 3

i) the incident ray, the normal and the reflected ray all lie in the same plane.
ii) the angle of incidence is equal to the angle of relection, or i=r

Question 4

Real image

Answer 4

An image that is formed by the actual intersection of rays and can be formed on a screen

Question 5

Virtual image

Answer 5

An image that is formed by the apparent intersection of rays and cannot be formed on a screen

Question 6

Parallax

Answer 6

Is the apparent movement of the object relative to another due to the actual movement of the observer.

Question 7

Spherical mirrors

Answer 7

Are cut from a sphere. They can be concave or convex.

Question 8

Concave mirrors

Answer 8

Have a real focus
If the object is outside the focus, the image is real & in front of the mirror
If the object is inside the focus, the image is virtual and behind the mirror

Question 9

Convex mirrors

Answer 9

The focal point of the mirror is virtual.

The image is always virtual, erect, diminished and behind the mirror.

Question 10

Focal length

Answer 10

Is the distance from the pole of the mirror to the focus. It is equal in length to half the mirror’s radius of curvature.

Question 11

Magnification

Answer 11

The mag. of an image is the ratio of the height of the image to the height of the object

Question 12

Refraction

Answer 12

The bending of light as it goes from one medium to another.
If the second medium is denser, the light will bend towards the normal.
If it is rarer, the light will be refracted away from the normal

Question 13

Law of refraction

Answer 13

i) the incident ray, the normal ray and the refracted ray all lie in the same plane
ii) the ratio of the sine of the angle of incident to the sine of the angle of refraction is a constant(snell’s law)

Question 14

Refractive index

Answer 14

The refracted index of a medium is the ratio of the sine of the angle of incidence to the sine of the angle of refraction when light travels from a vacuum(or air) into that medium.

Question 15

Critical angle

Answer 15

The angle of incidence in a denser medium when the angle of refraction in the rarer medium in the rarer medium is 90 degrees

Question 16

Total internal reflection

Answer 16

Occurs when the angle of incidence in the denser medium is greater than the critical angle. The light is fully reflected at the boundary of the two media and does not enter the second medium at all.

Question 17

Optic fibre

Answer 17

A very thin strand if transparent material (usually glass), through which light travels by total internal reflection.

Question 18

Light or visible light

Answer 18

The part of the electromagnetic spectrum to which our eyes are sensitive. The visible light has a wavelength between 400nm and 700nm approximately. Light is a form of energy as can be demonstrated by the revolving vanes of a crooke’s radiometer when light shines on them light travels at 3x10^8 ms^-1