Light 💡

Question 1

How to you measure the the angles of incidence and reflection?

Answer 1

You have to measure them from a line at right angles to the mirror known as the normal.

Question 2

What does the law of reflection state?

Answer 2

I= R

Angle of incidence = angle of reflection

Question 3

What are the properties of an image in a plane mirror?

Answer 3

The image in a plane mirror is:

The image is laterally inverted;

The same height as the object;

as far behind the mirror as the object is in front;

virtual.

Question 4

What is a virtual image?

Answer 4

A virtual image is an image from which rays of light appear to diverge, and do not actually pass through.

A virtual image cannot be formed on a screen.

Question 5

How do you find the position of an image in a plane mirror?

Answer 5

Draw a pencil line across the top of a sheet of white paper. Mark points A and B on the line and draw a straight dotted line down from A and B. Select a position for the object and label that O.

Draw a line from O to the closest corner of A to O and reflect the line off the pencil line. Do this for B aswell.

Now extend the reflected rays behind the mirror(the pencil line) as dotted lines until they meet at point. This is where the image was formed. Label the point I. These dotted lines are called virtual rays.

Question 6

What happens when light travels from air into glass?

Answer 6

Light will slow down as glass is more dense than air.

Light will bend towards the normal when moving from air to glass.

One way of remembering this is to use the word FAST.

If light gets Faster it bends Away from the normal.

If light gets Slower it bends Towards the normal.

Question 7

What happens when light moves from glass to air?

Answer 7

Light will speed up and will bend away from the normal.

Question 8

What happens when light moves from air to water?

Answer 8

Light will slow down and bend towards the normal.

Question 9

What happens when light moves from water into air?

Answer 9

Light will speed up and bend away from the normal.

Question 10

What is refraction?

Answer 10

The change in direction of a beam of light as it travels from one material to another.

Question 11

How does the amount of refraction of light relate to the change of speed of light?

Answer 11

The greater the refraction, the larger the change of speed of the light is.

(The change of speed of light is directly proportional to the refraction of light).

Question 12

Why can a spectrum of light be produced in a prism?

Answer 12

This is because different colours of light travel at different speeds in the glass.

Question 13

What is dispersion?

Answer 13

Dispersion is the splitting of white light into its component colours using a prism because the different colours of light change speeds by different amounts and therefore refract by different amounts.

Question 14

What are the colours of the rainbow in order?

Answer 14

ROYGBIV

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

Question 15

What are the 2 types of lenses?

Answer 15

A lens can be converging (convex) or diverging (concave).

Question 16

What is a converging lens?

Answer 16

A converging lens also known as a convex lens.

A converging lens is thicker in the middle than it is at the edges.

Parallel light rays that enter the lens converge.

They come together at a point on the principal axis called the principal focus F.

The centre of the lens is called the optical centre C.

A ray of light incident at the optical centre passes straight through without being bent.

Question 17

What is a diverging lens?

Answer 17

A diverging (concave) lens is thinner in the middle than it is at the edges. This causes parallel rays to diverge.

They separate but appear to come from a principle focus F on the other side of the lens.

In a ray diagram, a diverging (concave) lens is drawn as a vertical line with inward facing arrows to indicate the shape of the lens.

Question 18

How do you carry out an experiment to measure the focal length of a converging lens using a distant object?

Answer 18

Point the lens at a distance object outside the window – for instance a tree or building. The greater the distance the better. Rays of light from this object are taken to be parallel as the object is assumed to be at infinity.

Move the position of the screen behind the lens until a sharp image is formed on it.

Parallel rays of light form an image at the principal focus of a lens, and so the screen is at the principal focus. The distance between the optical centre of the lens and the screen is the focal length, f.

Measure this distance with a 30 cm rule and record in a suitable table.

Repeat the process several times and calculate the average focal length.

Question 19

What is a real image?

Answer 19

A real image is an image that can be projected onto a screen.

Rays of light actually pass through the image.

Question 20

What would an image in a camera or human eye be?

Answer 20

Cameras and eyes contain convex lenses.

For a distant object that is placed more than twice the focal length from the lens, the image is:

between F and 2F on the opposite side of the lens to the object;

inverted;

diminished;

real.

Question 21

What would an image in a projector be?

Answer 21

Projectors contain convex lenses. For an object placed between one and two focal lengths from the lens, the image is:

further away than 2F on the opposite side of the lens to the object;

inverted (upside down);

enlarged;

real.

In a film or data projector, this image is formed on a screen.

Film must be loaded into the projector upside down so the projected image is the right way up.

Question 22

What would an image formed in a magnifying glass be?

Answer 22

A magnifying glass is a convex lens used to make an object appear muchlarger than it actually is.

This works when the object is placed at a distance from the lens of less than one focal length. The image is:

on the same side of the lens as the object, but further away;

upright;

enlarged;

virtual.