Answers to Light 2007NYGH/Sec3IP/EOYP2Q5 1(a)

C Fig. 5.1 (b) (i)

IA IB

(ii) B appears to run towards A/C along a straight line. 2. a (i) Critical angle = sin-1(1/1/5) = 42o [1] (ii) Angle of refraction = sin-1 (sin 40o/1.5) = 25o [1] (iii) Angle of emergence = 50o [1]

Mirror M

A B

Fig. 5.2

C

ray from IB to A---- 1 mark ray from B to C-----1 mark dotted ray from IB to C----1 mark

Mirror M Dance studio wall Dance studio wall

Two image drawn correctly award 1 mark

1

(iv)

b. The prism does not have a silver backing like mirror which may peel off with age. The prism allows more light energy (stronger intensity) to enter the room. Multiple-reflections will occur at glass surfaces of the mirror which will reduce the light intensity entering the room.

c. The setup will allow light rays that strike the surface from angle of incidence from 0o (shown by

the blue ray) to an angle of 90o(shown by the red ray) to enter the room.

Fig. 10.2

50

A

B C 45

25o

70o

70o

25o

50o

45

A

B C

2007NYGH/Sec3IP/EOYP2Q6 3 The diagram in Fig. 6 shows a ray of light from a point object O striking a converging lens L. The lens forms an image at point I.

b. An upright, virtual and magnified image is formed. 2007NYGH/Sec4IP/EOYP2Q4 4 n= 1/sin c

1.6 = 1/sin c c= sin-1(1/1.6) =39 n = sin i /sin r 1.6 = sin i /sin 21 i = sin-1 [1.6x sin 21] = 35 Path of incident ray drawn correctly Path of refracted ray drawn with correct angle r

B1 B1 B1 B1

2007NYGH/Sec4IP/EOYP2Q5 5(a) f = 12 cm A1 (b) 2 types of rays drawn

One ray through centre One ray parallel to the centre ray correct symbol of the lens, image, arrow heads, and principal axis

B1 B1

(c) 1/u + 1/v = 1/f 1/24 + 1/v = 1/12 v = 24 cm

B1 B1

2007NYGH/Sec4Olvl/PrelimP2Q4 6 (a) Critical angle is incidence angle in optically denser medium for which the angle of

refraction is 90 / refracted ray emerges along the boundary of the 2 media. [1]

O

I

X

Fig. 6

L

60 35

21 39

Lens

Image

Focal plane

Parallel rays from distant object

F

(b) cw = 39 [1] R.I. = 1/sin cw [1] = 1.59 [1] (ignore s.f.)

(c) No penalty if angles not labelled. If angles labelled correctly but drawn wrongly, accept it as correct. 1m for refraction at Q and T (correct angles of refraction determined) 1m for reflection at R ( i = r) 1m for total internal reflection at S (i=r)

P

Q

28.8 48 48 67 67 23 38.4

R

S

T

50