Extra Questions On Reflection and Refraction of Light
Reflection is the bouncing back of light when it strikes on a polished surface like mirror.
Laws of Reflection: (1) Angle of incidence is equal to the angle of reflection.
(2) The incident ray, the reflected ray and the normal at the point of incidence, all lie in the same plane.
Spherical Mirrors: Mirrors whose reflecting surface is curved. There are two types of spherical mirrors- (i) Convex and (ii) Concave mirror
Bending of light when it enters obliquely from one transparent medium to another.
Cause of refraction: Change in speed of light.
Some examples of refraction :
(i) The bottom of swimming pool appears higher.
(ii) A pencil partially immersed in water appears to be bent at the interface of water and air.
(iii) Lemons placed in a glass tumbler appear bigger.
(iv) Letters of a book appear to be raised when seen through a glass slab.
Snell’s law : The ratio of sine of angle of incidence to the sine of angle of refraction is a constant, for a light of given colour and for a given pair of media.
Q.1. List four properties of the image formed by a plane mirror.
AnswerAnswer. Properties of image formed by a plane mirror:
1. It is always virtual and erect.
2. Its size is equal to that of the object.
3. It is formed at the same distance behind the mirror as the object is in front of the mirror.
4. It is laterally inverted.
Q.2. List four properties of the image formed by a convex mirror.
AnswerProperties of image formed by a convex mirror:
1. It is always formed behind the mirror, between the pole and its focus.
2. It is always virtual and erect.
3. Its size is always smaller than the object.
4. Magnification is always positive.
Q.3. List four properties of the image formed by a concave mirror, when object is placed between focus and pole of the mirror.
Answer1. The image is formed behind the mirror.
2. It is enlarged, he. magnified.
3. It is virtual.
4. It is erect.
Q.4. Redraw the given diagram and show the path of the refracted ray:
Q.5. Redraw the given diagram and show the path of the refracted ray:
Q.6. Draw the following diagram in your answer book and show the formation of image of the object AB with the help of suitable rays.
Q.7. Which kind of mirrors are used in the headlights of a motor-car and why?
AnswerConcave mirror, to get the parallel beam of light.
Q.8. Explain with the help of a diagram, why a pencil partly immersed in water appears to be bent at the water surface.
AnswerLight from different points on the pencil, immersed in water refracts and appears to come from a point above the original position.
Q.9. Name the type of mirror used in the following situations:
(i) Headlights of a car (ii) Rear-view mirror of vehicles (iii) Solar furnace Support your
answer with reason.
AnswerType of mirror used in (i) Headlights of a car: Concave mirror
Concave mirror is used because light from the bulb placed at the focus of it gets reflected and produces a powerful parallel beam of light to illuminate the road.
(ii) Rear view mirror of vehicles: Convex mirror Convex mirror is used because it always produces a virtual, and erect image whose size is smaller than the object. Therefore it enables the driver to see wide field view of the traffic behind the vehicle in a small mirror.
(iii) Solar furnace: Concave mirror
Concave mirror has the property to concentrate the sunlight coming from sun along with heat radiation at its focus. As a result, temperature at its focus increases and the substance placed at the focal point gets heated to a high temperature.
Q.10. A concave lens has focal length of 20 cm. At what distance from the lens a 5 cm tall object be placed so that it forms an image at 15 cm from the lens? Also calculate the size of the image formed.
AnswerAnswer: u=-60 cm; size of image = 1.25 cm; Image is diminished and virtual.
Q.11. An object 50 cm tall is placed on the principal axis of a convex lens. Its 20 cm tall image is formed on the screen placed at a distance of 10 cm from the lens. Calculate the focal length of the lens.
AnswerAnswer: f=7.15 cm
Q.12. Draw the ray diagram in each case to show the position and nature of the image formed when the object is placed:
(i) at the centre of curvature of a concave mirror
(ii) between the pole P and focus F of a concave mirror
(iii) in front of a convex mirror
(iv) at 2F of a convex lens
(v) in front of a concave lens
AnswerAnswer: (i) Nature of image: Real, inverted and same size
Image is formed at the centre of curvature.
(ii) Nature of image: Virtual, enlarged and erect
Image is formed behind the mirror.
(iii) Nature of image: Virtual, erect and diminished, image is formed behind the mirror.
(iv) Nature of image: Real, inverted and size to size, image is formed at 2F on the other side of lens.
(v) Nature of image: Virtual, erect and diminished image is formed between O and F on the same side of object.
Q.13. If a light ray IM is incident on the surface AB as shown, identify the correct emergent ray.
AnswerRay NQ, as it has to be parallel to ray OS.
Q.14. Draw ray diagrams to represent the nature, position and relative size of the image formed by a convex lens for the object placed:
(a) at 2F1
(b) between F1 and the optical centre O of lens:
Answer(a) Nature: Real, Inverted, Same size
Position: at 2F
(b) Nature: Virtual, erect and enlarged
Position: On the same side of the lens
Q.15. A ray of light, incident obliquely on a face of a rectangular glass slab placed in air, emerges from the opposite face parallel to the incident ray. State two factors on which the lateral displacement of the emergent ray depends.
AnswerLateral displacement depends on the:
angle of incidence, thickness of slab, and refractive index of the material
Frequently Asked Questions – FAQs
What is light?
Light is the form of energy that enables us to see.
State some properties of light.
- Electromagnetic wave, so does not require any medium to travel.
- Light tends to travel in straight line.
- Light has dual nature i.e., wave as well as particle.
- Light casts shadow.
- Speed of light is maximum in vacuum. Its value is 3 × 108 ms-1.
What happens when light falls on a surface?
When light falls on a surface, following may happen :
What is image?
Image is a point where at least two light rays actually meet or appear to meet.
What is lateral inversion?
The right side of the object appears left side of the image and vice-versa.
What is Principal axis?
It is line joining the pole and center of curvature.
What is Pole (P) of a mirror?
It is the centre of the spherical mirror.
What is Aperture of a mirror?
It is the effective diameter of the spherical mirror.
What is the relation between focal length and radius of curvature?
What is the optically rarer medium?
Out of two given media, the medium with lower value to refractive index.
What is the optically denser medium?
Out of two given media, the medium with higher value of refractive index.
What is the power of a lens?
It is defined as the reciprocal of focal length (in meter).
What is the dioptre?
1 dioptre is the power of lens whose focal length is one meter.