Week 4 – for 9th Std

I. Light and Sound Questions

  1. Try to make a periscope using two plane mirrors. (You can find mirrors in the do and discover science kit box) – Post your photo if you are able to make it!
  2. Observe the base of a water filled bucket. What do you observe?
  3. Fill a beaker with water. Put a pencil in the water. Why does it appear bent?
  4. Write law of reflection. Is it valid for plane, concave, convex, mirror? Is it valid for a wall?
  5. What is nearsightedness?
  6. What is ultrasonic sound? What is supersonic?
  7. If we get an echo from a big mountain after 1 second, how far is the mountain from us?
  8. Draw a ray diagram showing how the ray of light going towards apex of a prism will go through it
  9. Draw ray diagram for an object (vertical arrow) kept in front of a concave mirror between f and 2f.
  10. What is refractive index?
  11. Understand the ray diagram for a telescope and a microscope. Try to draw.
  12. What is total internal reflection?
  13. Explain longitudinal wave. What is frequency? What is wavelength?
  14. What is the effect of change in frequency on sound?

II. Newton disc

Observe the video (Newtons colourful disc appears white when rotated.) What can you conclude? Why does this happen?

Students who have bought the electricity kit box:

  1. Make and paint Newtons disc on a card paper. (colour lightly with crayons, don’t use dark colours)
  2. Use the battery and electric motor to rotate the disc!

Make your own newtons disc! Post your photo / video if you are able to make it! Here is a fantastic disc made by a 6th Std student –

Newtons Disc made by Ishil Bhatia

III. Videos on various principles of light:

i) Mixing of Light Vs Pigments – (Video)

  1. Which 3 colours are primary colours?
  2. Why are they called primary?
  3. Are black and white also colours? Do we see them in a rainbow?
  4. What difference do you observe in the mixing of different coloured lights and that of pigments?

ii) Mirror Video

In this video, observe the image of the man and the boy in a huge mirror. Observe that when the man puts light on the image, his image puts light on the boy! And vice-versa!

  1. Which type of mirror is this?
  2. What is the property of the image in this mirror?
  3. What are the uses of this type of mirrors?

iii) Light beam passed through water in a tank (video)

Light travels in the straight line. See the beam of light going in a straight line. Also observe the green laser path. It gets reflected from the top surface of the water. (This is called total internal reflection)


iv) Observe the video: The water is falling from a hole made to the water bottle. Observe that the green light travels with the water and bends too! (instead of going in a straight line). Explain why this happens.

Students can try doing this at home. Use red laser pointer which is available in stationery shops. Do this under parents OBSERVATION. Take CARE. The laser beam should NEVER enter anyone’s eye.


IV. Tuning Fork Sound – Video

Tuning fork produces ‘Quieeeeeee’ sound. And sound is produced due to vibration. Observe the video. The tuning fork is made to vibrate and put into water. Enjoy the vibrations in slow motion!