# Break a Pencil Magic: School Science Physics Experiment | Summary and Q&A

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December 13, 2017
by
LearnoHub - Class 11, 12
Break a Pencil Magic: School Science Physics Experiment

## TL;DR

When a pencil is dipped into water, it appears broken due to the bending of light as it travels from water to air.

## Key Insights

• 🙂 Light bends when it encounters a change in medium, which is why the pencil appears broken when submerged in water.
• 🙂 The brain interprets the rays of light as coming straight, leading to the perception of a bent pencil.
• 🙂 The thickness of the submerged part of the pencil appears to increase due to the convergence of light rays.
• 🙂 Refractive indices play a role in determining the degree of bending in the light rays.

## Transcript

we can make a pencil look broken even without breaking it interesting right all you need to do is dip a pencil into a glass of water and you see a broken pencil let us try to understand the science behind this broken pencil the science behind this broken pencil is based on one simple fact whenever light encounters a change in medium it bends so her... Read More

### Q: Why does a pencil dipped in water appear broken?

The light from the submerged part of the pencil bends as it leaves the water and enters the air, creating the illusion of a broken pencil.

### Q: How does the brain interpret the bent appearance of the pencil?

Our brain assumes that the rays of light reaching our eyes must be coming straight, so it interprets the bent rays as indicating that the pencil is actually bent.

### Q: Why does the submerged part of the pencil appear thicker in water?

The rays of light from the submerged part converge as they leave the water, creating the illusion of an increased thickness.

### Q: What determines the degree of bending in the light rays?

The degree of bending depends on the refractive indices of the two mediums, with light bending away from the normal as it goes from a denser medium (water) to a less dense medium (air).

## Summary & Key Takeaways

• When light encounters a change in medium, such as from water to air, it bends.

• For the parts of the pencil above water, the light travels straight and reaches our eyes without bending.

• For the parts of the pencil below water, the light bends as it travels from water to air, creating the illusion of a broken pencil.