Revision for Light

Which of the following does not reflect light?

• tennis ball

• unlit torch

• giant star

• rubber band

Answer explanation

Giant star is the only option which is a light source. Hence, we see the light source directly when its light ray travel to our eyes. Only non-light sources (tennis ball, unlit torch and rubber band) will have the light from source reflected off the object into our eyes to be seen.

Which is not a possible shadow of this object?

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Answer explanation

For 4, this is not possible, as the cup is made up of a smaller rectangular base and the main cup's oval body, hence the shadow must at least be made up of these 2 parts, and should not only rectangular in shape. Option 3 is possible if light is shining at top view of cup. Also, option 2 is possible, as handle may be hidden behind cup, and therefore not formed as part of shadow.

The shadow of the coconut tree will change throughout the day, depending on the position of the sun. Look at the shadows formed at timings A, B and C. Which timings do these likely occur at?

Hint: Refer to the compass direction to guess position of sun creating the relevant shadows!

• A: 9.30am

  B: 12pm

  C: 5pm

• A: 8pm

  B: 12pm

  C: 5am

• A: 10pm

  B: 1pm

  C: 5am

• A: 5pm

  B: 12pm

  C: 9.30am

Answer explanation

The sun rises around 7am and sets around 7pm, hence the options 2 and 3 are out, since no shadow seen at 8pm, 10pm, 5am (before sun rises or after sun sets).

Option 1 is correct, since the sun must be opposite direction (ie. sun is in east) of shadow at A, and hence A will be seen in morning. Also, sun will be in opposite direction (ie. sun is in west) of shadow, and hence C will be seen in evening.

Construction workers wear the following vest with has a reflector, when working on the roadside at night. Why is this so? Select the only true statement.

• The reflector gives out light and allows oncoming drivers to see the workers' vests clearly.

• The reflector should be made of a material that best allows light to go through it, like clear plastic.

• The reflector should be made of a material that reflects light best.

• The reflector should help conduct heat well, so that the workers can keep warm while working.

Peter shines a torch on a bunch of grapes and its shadow is formed on a screen. How can he enlarge the shadow of the grapes? Select ALL possible answer(s).

• Move the grapes further from the torchlight

• Move the grapes nearer to the torchlight

• Move the torchlight nearer to the screen

• Move the grapes nearer to the screen

Janet shines the torch through different liquids X, Y and Z and records the light that is able to pass through it.

If X allows the most light through it, and Z blocks the most light, which liquid (X, Y, Z) will have the highest reading for the datalogger?

• X

• Y

• Z

• All will have the same reading

The torch shines directly in a straight line to the wooden cone and frosted glass. Which do you think is the possible shadow formed on the screen?

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Answer explanation

Frosted glass is translucent and allows some light to pass through, resulting in a less dark shadow at the top. Wooden cone is opaque and blocks all light, resulting in a darker triangular shadow at bottom.

Karen shines a torch at object A, which is made of 3 different materials X, Y and Z.

The shadow formed on the screen for these 3 materials is seen on the screen. Please select the correct materials for X, Y and Z.

• X: Frosted Glass

  Y: Wood

  Z: Clear Plastic

• X: Tracing Paper

  Y: Rubber

  Z: Clear Plastic

• X: Rubber

  Y: Clear Plastic

  Z: Frosted Glass

• X: Frosted Glass

  Y: Clear Plastic

  Z: Rubber

Answer explanation

X has light shadow and should be translucent (some light pass through)(Eg. frosted glass/ tracing paper).

Y has no shadow and should be transparent (most light pass through) (eg. clear plastic).

Z has darkest shadow and should be opaque (no light can pass through)(eg. wood/ rubber)

When the rectangular block of wood is shifted from position 1 to 2, then 3 and 4, the shadow size will change. Which graph is correct?

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Answer explanation

Position 1 is further from torch, so shadow should be smallest. Position 4 is neares to torch, so shadow should be biggest. The graph should show an increasing gradient/ trend.

Which one of the following objects could NOT have possibly formed the attached shadow formed?

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Answer explanation

The triangular pyramid will form a triangular shadow, not rectangle-shaped shadow.

For the other shapes, depending on the orientation of the object, it is possible to form a rectangle-shaped shadow.