On an optical bench a point object is placed at the mark of 10 cm, a convex lens of focal length 15 cm at the mark of 40 cm and a concave lens of focal length 15 cm placed at the mark of 60 cm. The final image is formed at the mark of: (point object and two lenses are coaxial)
1. 30 cm
2. 80 cm
3. 90 cm
4. infinity
Two similar plano-convex lenses are combined together in three different ways as shown in the adjoining figure. The ratio of the focal lengths in three cases will be:
1. 2 : 2 : 1
2. 1 : 1 : 1
3. 1 : 2 : 2
4. 2 : 1 : 1
A glass sphere of radius 12 cm has a small mark at a distance of 3 cm from its centre. Where will this mark appear when it is viewed from the side nearest to the mark along the line joining the centre and the mark?
1. | 8 cm inside the sphere | 2. | 12 cm inside the sphere |
3. | 4 cm inside the sphere | 4. | 3 cm inside the sphere |
Focal length of objective lens and eyepiece of an astronomical telescope are 200 cm and 10 cm respectively. The length of telescope for maximum magnification is nearly:
1. 207 cm
2. 210 cm
3. 204 cm
4. 220 cm
A liquid of refractive index 1.33 is placed between two identical plano-convex lenses, with refractive index 1.50. Two possible arrangements, P and Q, are shown. The system is:
1. | divergent in P, convergent in Q | 2. | convergent in P, divergent in Q |
3. | convergent in both | 4. | divergent in both |
The diameter of the eye-ball of a normal eye is about 2.5 cm. The power of the eye lens varies from:
1. 2 D to 10 D
2. 40 D to 32 D
3. 9 D to 8 D
4. 44 D to 40 D
An object is placed at a point distance \(x\) from the focus of a convex lens and its image is formed at \(I\) as shown in the figure. The distances \(x\) and \(x'\) satisfy the relation:
1. \(\frac{x+x'}{2} = f\)
2. \(f = xx'\)
3. \(x+x' \le 2f\)
4. \(x+x' \ge 2f\)
A ray of light falls on a prism ABC (AB=BC) and travels as shown in figure. The refractive index of the prism material should be greater than:
1. | \(4 /{3}\) | 2. | \( \sqrt{2}\) |
3. | \(1.5\) | 4. | \( \sqrt{3}\) |
A fish is a little away below the surface of a lake. If the critical angle is \(49^{\circ}\), then the fish could see things above the water surface within an angular range of \(\theta^{\circ}\) where:
1. \(\theta = 49^{\circ}\)
2. \(\theta = 90^{\circ}\)
3. \(\theta = 98^{\circ}\)
4. \(\theta = 24\frac{1}{2}^{\circ}\)
To increase the magnifying power of a telescope:
1. | The focal length of the eyepiece should be increased. |
2. | The focal length of the objective should be increased. |
3. | The wavelength of light should be increased. |
4. | The aperture of the eyepiece should be increased. |