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Numerical Problem on Light Reflection and Refraction
(More numerical and questions at this page) Q1: How fast does the light travel in a glass of refractive index 1.5?
Answer: By Snell's law, refractive index (n) is the ratio of i.e.
Q2:When a bright object is placed 10 cm away from a concave mirror, its real image is formed at a distance 40cm from the mirror. What is the focal length of the mirror?
Answer:
Q3: If the angle of incidence of a ray of light falling on the glass surface is 30° and the angle of refraction is 19°. what is the refractive index of glass?
Ans: angle of incidence i = 30°
angle of refraction r = 19°
refractive index n = sin i/sin r = sin 30/sin 19
n = .5/.3256 = 1.535 ....(ans)
Q4: If a child crawls towards a mirror at a rate of 0.20 m/s, then at what speed will the child and her image come nearby to each other?
Ans: In 1 sec, the child moves towards the mirror by a distance of 0.20 meters. In the same second, her image also moves 0.20m closer.
Therefore, the child and her image comes closer to each other by 0.40m per second.
1. Light is a form of energy. Since energy cannot be seen, we see objects in light.
2. A ray of light is a straight line which represents the path of traveling light. A collection of light rays is called a beam of light.
3. Q: How do we see objects?
Ans: The visual ability of humans is the
result of the complex interaction of light, eyes and brain.
We are able to see because light from an object can move
through space and reach our eyes. Once light reaches our
eyes, signals are sent to our brain, and our brain deciphers
the information in order to detect the appearance, location
and movement of the objects we are sighting at.
4. Luminous
objects are objects that generate their own
light. e.g. firefly, the sun.
5. Illuminated
objects are objects that are capable of
reflecting light to our eyes. e.g. the moon
6. A ray of light that falls on a surface is called incident ray.
7. The light that is sent back by the reflecting surface is called reflection.
8. The ray that is sent back by the reflecting surface is called the reflected ray.
9. When light falls on a body, it may be absorbed, may be transmitted or light may come back to the same medium.
10. Laws of Reflection (watch the you tube video):
a. First law of reflection: The incident ray, the normal to the surface at the point of incidence and the reflected ray, all lie in the same plane.
b. Second law of reflection: The angle of incidence is equal to the angle of reflection.