# Physics 2018 | Study Mode

Question 21
A
splits into three components after rainfall
B
is dispersed by glass prisms
C
splits into its constituent colours before rainfall
D
is dispersed into its constituent colours after rainfall
##### Explanation

A rainbow is caused by the dispersion of sunlight by tiny water droplets present in the atmosphere, which can be seen after the rain.

Question 22
A
converging meniscus
B
plano-convex
C
diverging meniscus
D
bi-convex
##### Explanation

The diagram is that of a plano-convex lens; a type of converging lens.

Question 23
A
30
B
45
C
60
D
90
##### Explanation

Formula for number of images = $$\frac{360}{n} - 1$$

where n is the angle of inclination.

Given the number of images = 11, we have

$$\frac{360}{n} - 1 = 11$$

$$\frac{360}{n} = 12$$

$$n = \frac{360}{12} =30$$

Question 24
A
frequency
B
tension in a vibrating string
C
mass of a vibrating string
D
amplitude of sound wave

Question 25
A
electroscope
B
electrophorus
C
capacitor
D
cell
##### Explanation

Most capacitors contain at least two electrical conductors often in the form of metallic plates or surfaces separated by a dielectric medium.

Question 26
A
a.c. generator
B
a.c. motor
C
d.c. generator
D
d.c. motor

Question 27
A
1358mm
B
957mm
C
760mm
D
638mm
##### Explanation

Let $$h_{Q}$$ and $$\rho_{Q}$$ be the least length and the density of $$Q_{1}$$

while $$h$$ and $$\rho$$ are the length and density of mercury respectively.

$$h\times \rho \times g = h_{Q} \times \rho_{Q} \times g$$

$$76cm \times 13.6 \times 10 = h_{Q} \times 16.2 \times 10$$

$$h_{Q} = \frac{76\times13.6\times10}{16.2\times10}$$

$$h_{Q} = \frac{10336}{162}$$

$$h_{Q} \approxeq 63.8cm = 638mm$$

Question 28
A
10.0N
B
20.0N
C
40.0N
D
50.0N
##### Explanation

Question 29
A
between the focus and the lens
B
at the focus
C
between the focal length and twice the focal length
D
beyond twice the focal length
##### Explanation

When the object is placed between the optical centre of the lens and the focal length, the image formed is virtual, erect and magnified.

Question 30
A
A and E
B
B and D
C
C and F
D
D and H