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Physics Form 4 Answers

(b) (i) Virtual image is image that Q2 m = = h i = 15 = 1.5 (c) The separation distance of the
v
cannot be displayed on the u h o 10 lenses
screen. Therefore, v = 1.5u = 40 + 5
(ii) = 1.5 × 2.0 m = 3.0 m = 45 cm
1 cm (d)
1
1
1
Converging lens Using + =
1 cm u v f 5 cm
1 1 1 5 Parallel rays 40 cm
f
2 + = = 6 from distant
3
Therefore, focal length f = 1.2 m object
1
1
F Main axis Q3 Using 1 + =
Image Object f = 2 cm u v f 1 Lens P Lens Q
1
1
1 = – = – 1 –
v f u 10 30
= – 4 Q3 Similarity:
30 • Consists of two convex lenses
Virtual image is image that v = –7.5 m • The eyepiece function as a
cannot be displaced on the 30 magnifying glass
screen = 2 cm v 4 1 Differences:
m = = = • For microscope in normal
Q2 (a) u 30 4 adjustment, the final image is at
The image is virtual, upright,
at a distance of 7.5 cm from near point. While for telescope in
the lens on the same side normal adjustment, the final image
as the object and has linear is at infinity.
Image 1 • The distance between the
magnification of .
F 4 objective lens and the eyepiece of
Q4 the microscope is L O > f O + f e . The
distance between the objective
v/cm lens and the eyepiece of the
telescope is L O ≤ f O + f e .
(b) The size of the image does not 60
change but the brightness of
image reduced by half. 50 u = v Checkpoint 6.6
Q3 (a) Convex lens 42 Q1 (a)
v
(b) M = = 30 = 0.5 40 P
u
60
(c) 30
Q
20
F F
10 R
u = 60 cm f = 20 cm
v = 30 cm 0 u/cm
10 18 20 30 40 50 60
Focal length, f = 20 cm (b) The image is real, inverted and
v 42 7
(a) m = = = = 2.33 magnified.
Checkpoint 6.4 u 18 3 (c) The image is nearer to the
1 1 1 (b) u = v = 25 cm mirror and becomes smaller in
Q1 (a) + =
u v f f = 25 size.
1 1 1 1 1 1 2
v = – = 20 – 30 = 60 = 12.5 Q2 (a)
f
u
v = 60 cm
v 60 Checkpoint 6.5
m = = = 2
u 30
Therefore, the image is real, Q1 (a) For distant objects, the image
must be formed at the focal
inverted, 60 cm from the lens, point of the lens. Therefore, the 25°
located opposite to the object distance between the lens and F C
and enlarged 2 times. the film is 50 mm.
1 1 1
(b) + = (b) The camera lens should be
u v f adjusted outward toward the
1 1 1 1 1 1
v = – = 20 – 15 = 60 object. As the object distance
f
u
v = –60 cm is reduced, the image distance (b) The image is at F.
increases. With this, the
v 60 distance between the lens and (c) The image is virtual, upright and
m = = 15 = –4 the film is slightly longer than diminished.
u
The image is virtual, upright, at 50 mm. Q3 • Focal length of mirror P = 12 cm.
a distance of 60 cm from the Q2 (a) Astronomical telescopes The image from distant object is
lens on the same side as the (b) Objective lens: lens P, Eyepiece: formed at the focal point of the
object and is magnified 4 times. lens Q mirror.
262
ANS FOC PHYSICF F4 1P.indd 262 29/01/2020 2:04 PM