Ray Optics and Optical Instruments

A person suffering from myopia is unable to see:

1. Nearby objects clearly
2. Distant objects clearly
3. Objects of only one colour
4. Bright objects only

A ray of light passes through the optical centre of a thin convex lens. It emerges:

1. Parallel to the principal axis
2. Without any deviation
3. Through the focus
4. At an angle of 90°

Two thin convex lenses of powers +3 D and +2 D are placed in contact. The focal length of the combination is:

1. 10 cm
2. 20 cm
3. 25 cm
4. 50 cm

A compound microscope has an objective lens of focal length 1 cm and an eyepiece of focal length 5 cm. If the tube length is 20 cm and the final image is formed at the least distance of distinct vision (25 cm), the magnifying power is:

1. 80
2. 100
3. 120
4. 150

An astronomical telescope in normal adjustment has an objective lens of focal length 100 cm and an eyepiece of focal length 5 cm. The magnifying power of the telescope is:

1. 10
2. 15
3. 20
4. 25

A prism has an angle of 60°. A ray passes through it under the condition of minimum deviation. Which statement is correct?

1. Angle of incidence equals angle of emergence.
2. Angle of refraction inside the prism is zero.
3. Angle of deviation becomes zero.
4. Angle of incidence is twice the angle of emergence.

The magnifying power of a simple microscope increases when:

1. Focal length increases
2. Focal length decreases
3. Aperture increases only
4. Object distance becomes infinite

An object is placed at twice the focal length of a convex lens. The image formed will be:

1. Real, inverted and same size
2. Virtual and magnified
3. Real and highly magnified
4. Virtual and diminished

The refractive index of a medium is 1.73. The critical angle for light travelling from this medium to air is closest to:

1. 25°
2. 35°
3. 45°
4. 60°

A convex mirror has a focal length of 20 cm. An object is placed 40 cm in front of the mirror. The image distance is:

1. +13.3 cm
2. -13.3 cm
3. +40 cm
4. -40 cm

An object is placed at the centre of curvature of a concave mirror. The image formed will be:

1. Virtual, erect and magnified
2. Real, inverted and of the same size
3. Real, diminished and inverted
4. Virtual and diminished

The power of a converging lens of focal length 50 cm is:

1. +1 D
2. +2 D
3. -2 D
4. +5 D

The critical angle for a glass-air interface is 42°. Total internal reflection will occur if the angle of incidence inside the glass is:

1. 30°
2. 35°
3. 42°
4. 50°

A convex lens has a focal length of 20 cm. An object is placed 30 cm in front of the lens. The image distance is:

1. 60 cm
2. 30 cm
3. 15 cm
4. 20 cm

A ray of light travels from air into a glass slab of refractive index 1.5 at an angle of incidence 30°. The angle of refraction is closest to:

1. 15°
2. 19.5°
3. 30°
4. 45°