1.0 um
1.1
Is this a plant or animal cell?
1.2
1.3
Provide labels for A, B and D.
Draw and label organelle C.
Use the following equation and calculate the width of the cell (X to Y).
Show all your working.
1.4
(1)
(2)
(3)
(6)
1.5
Actual size of object =
Measured length of scale line (mm)
(4)
(16)
Give TWO visible reasons for your answer in QUESTION 1.1. -
Measured length of object (mm) x length on scale (um)
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12th
Physics
Ray Optics and Optical Instruments
Combination of Lenses
Three lenses in contact hav...
PHYSICS
Asked on December 30, 2019 byRahamath Mudrabettu
Three lenses in contact have a combined focal length of 12cm. When the third lens is removed the combined focal length becomes 60cm. The third lens is :
A
a converging lens of focal length 30 cm
Your Answer
B
a converging lens of focal length 60 cm
C
a diverging lens of focal length 30 cm
Correct Answer
D
a diverging lens of focal length 60 cm
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VIDEO EXPLANATION

ANSWER
Let f1, f2 and f3 be three focal lengths of the lenses.
f=12
f1=f11+f21+f31
When the third lens is removed, f′1=f11+f21
f′=
f′=760
121=7601+f31
⇒f3=−30
Since f3 is negative, it is a diverging lens having focal length 30cm.
19. Three lenses in contact have a combined focal length of 12 cm. When the third lens is removed, the combined focal length is 60/7 cm. The third lens is
(1) A converging lens of focal length 30 cm
(2) A converging lens of focal length 60 cm
(3) A diverging lens of focal length 30 cm
(4) A diverging lens of focal length 60 cm