Light Travels In a Straight Line

Light travels in a straight line can be observed by keeping an object in the path of light. In an atmosphere which is bit dusty, we can see light traveling in a straight line. Light emerging from the torch, train and lamps always travel in a straight line. Let us study in detail how does light travel in a straight line.

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Light Travels Along a Straight Line

Life without light would have been pretty dull. Light travels at a speed of 186,000 miles per second. You must have observed that in your house that whenever a beam of light enters a dark room through a tiny hole in the window, the lightwave always travels in a straight line.

Let us carry out a small activity to show that lightwave travels along a straight line. Take three CD’s and align them together. Align them in such a way that all the CD’s line in a straight line. Now take a candle and place it at the other end. Do make sure that the tip of the candle and the holes of the CD’s all lie in the straight line. Ensure that the height of the CD’s and the tip of the candle are same. Observe the flame of the candle. We are able to see the flame of the candle because the light wave travels through the holes and reaches our eye.

Browse more Topics under Light

• Mirrors
• Reflection of Light
• Sunlight – White or Coloured
• Images Formed By Lenses

Now if suppose we displace the center of the CD’s we observe that we are not able to see the flame of the candle. Why does that happen? This is because the light gets blocked. If the light could have the ability to take a curve and travel, we could have seen the lightwave. But since light travels in a straight line, we were unable to see the flame of the candle when the CD is displaced. This proves that light travels along a straight line.

(Source: Wikipedia)

In the above picture, we can clearly see that light coming through the holes in the window travel along a straight line.

Questions For You

Q1. The phenomenon in which the moon’s shadow falls on earth,  or the earth casts its shadow on the moon, is known as

1. Shadow
2. Lateral deviation
3. Eclipse
4. Tides

Answer: C. The phenomenon in which the moon’s shadow falls on earth or the earth casts its shadow on the moon is known as an eclipse. During a solar eclipse, moon’s shadow falls on the earth. During a lunar eclipse, earth’s shadow falls on the moon.

Q2. Two examples of non-luminous objects are

1. Stars and Moon
2. Burning candle, glowing bulb
3. The moon, a spoon
4. Stars, a spoon

Answer: C. Non-luminous objects are those that do not emit light. The moon and the spoon do not emit light. So these two are good examples of non-luminous objects.

Q3. We can see the objects only when

1. Reflected light from the object reaches our eye.
2. The objects absorb all the light.
3. When the objects allow all the light to pass through them.
4. None of these.

Answer: A. Objects can only be seen when light falls on the object and are reflected back to our eyes.