CH 1- Light

Question 1

Laws of reflection of light

Answer 1

Law 1: the incident Ray, the normal at the point of incidence and the reflected Ray all lie on the same plane

Law 2: the angle of incidence is equal to the angle of reflection (i=r)

Question 2

Virtual image

Answer 2

Image formed by the apparent intersection of Ray’s
Is the same distance behind mirror as object in front
On perpendicular from object to mirror

Question 3

Parallax

Answer 3

The apparent movement of one object relative to another to to the motion of the observer
Object farthest appears to move

Question 4

Reflection

Answer 4

The bouncing of light off an object

Question 5

When objects are in a state of no parallax they must be

Answer 5

In the same line and the same distance from the observer

Use this to locate image of object in plane mirror

Question 6

Real image

Answer 6

Image formed by the actual intersection of Rays

Can be located by screen or method of no parallax

Question 7

For a concave mirror

Answer 7

If image is outside focus it is real and located in front of the mirror

If real: 1/u + 1/v = 1/f

If image is inside or at focus it is virtual and behind mirror

If virtual: 1/u - 1/v = 1/f

Question 8

MAGNIFICATION

Note:when finding m, v is always positive as distance is always positive

Answer 8

Magnification =

height of image Image distance
—————- = —————
height of object Object distance

Magnification= v/u

Question 9

For a convex mirror

Answer 9

Image is always virtual and located behind mirror

Image is always diminished- the nearer to the mirror the object is the bigger the image

1/u - 1/v = - 1/f

Question 10

Refraction

Answer 10

The bending of light as it passes from one medium to another

Question 11

1) when light travels from a rarer to a denser medium it is refracted ______
2) when light travels for a denser to a rare medium it is refracted _____

Answer 11

1) towards the normal

2) away from the normal

Question 12

Laws of refraction of light

Law 1 and snell’s law

Answer 12

Law 1) the incident Ray, the normal at the point of incidence and the refracted Ray all lie on the same plane

Law 2) the ration of the sine of the angle of incidence to the sine of the angle of refraction is a constant, n

n is the refractive index between two media

Question 13

Refractive index of a medium

Answer 13

The ratio of the sine of the angle of incidence to the sine of the angle of refraction when light travels from a vacuum into that medium

Question 14

For any two media x and y

xNy = 1 / yNx

Answer 14

aNg = sin i
—–
Sin r

gNa = sin r
—–
Sin i

Question 15

Refractive index of a medium

Answer 15

Apparent depth

Of object
( when viewed from air with perpendicular line of view)

Question 16

If the speed in medium one is c1 and the speed in medium two is c2 it follows that ___

Answer 16

1n2 = C1
—
C2

ie:

C1. Sin i
— = —–
C2. Sin r

It follows that refractive index of a medium= speed of light in air over speed of light in medium

Question 17

Critical angle

Answer 17

When light travels from a denser to a rare medium the angle of incidence whose corresponding angle of refraction is 90 degrees is Called the critical angle (C) for those two media

Question 18

Total internal reflection

Answer 18

When light going from a denser to a rarer medium strikes the second medium with an angle of incidence greater than the critical angle, it is reflected back into the denser medium, this is called TIR

Question 19

Refractive index of a medium

Answer 19

SinC

Question 20

Optical fibre

Answer 20

A very thin transparent rod through which light can travel by total internal reflection

Question 21

Transmission of light through optical fibre

Answer 21

Light enters fibre and strikes inside at angle greater than critical angle

Ray is reflected to opposite side and TIR occurs again

This process continues and light travels

Dangers:
If fibre is bent through too large an angle light can escape

Light can escape when it comes into contact with another fibre or itself

Question 22

How to overcome flaws of fibre optics

Answer 22

Coat fibres in material of lower refractive index

Question 23

Uses and advantages of optical fibres

Answer 23

Telephones- light pulses

Energy losses in optical fibres are smaller than losses in electrical cables

Optical fibres smaller than electrical

Much less interference

Question 24

Mirages

Answer 24

Refractive index of air changes with temperature
This causes mirages
Road absorbs heat and heats air above it
Hot air is thinner than cold and has lower refractive index
Light swerves
Goes down and up

Question 25

For a convex LENS

Answer 25

If the object is outside the focus the image is real and located on the opposite side of the lens
It is inverted

If the object is inside the focus it is virtual image and located on same side of lens as object
Image is upright

Question 26

Formula for lenses

Answer 26

For convex-
Real 
1 / u + 1 / v = 1 / F
Virtual 
1/u - 1/v  =   1/f

For concave-

1/u - 1/v = - 1/f

IT IS THE OPPOSITE TO MIRRORS
CONCAVE MIRROR COULD BE BOTH
CONVEX LENSES CAN BE BOTH

Question 27

Power of a lens

Answer 27

Focal length

Per meter

Shorter the focal length the greater the power of the lens

Question 28

If two lenses of power p1 and p2 are placed together the power P of the combination is

P= p1 + p2

Answer 28

If two lenses of focal length f1 and f2 are placed in contact the total focal length is

1/f = 1/f1 + 1/f2 where f is + for convex and - for concave

Question 29

Power of accommodation

Answer 29

Is they eyes ability to focus a real image of an object on the retina, whether the object is far or near to the eye