April – Sir Isaac Newton – Concave and convex mirror experiment

I was eating my lunch, as i was waiting for it to finish cooking I looked at the spoon that I would be eating it with. As I looked into the spoon I noticed that it had both a convex and concave mirror. I noticed that the concave side flipped me up-side-down and the other (convex) made my face seem small in comparison to my real size.

"concave" (left) "convex" (right)

This intrigued me. I thought that if a spoon was able to have these shapes and make these changes, what does light do? I decided that I would look in to it further, so as I ate my lunch I planned out my experiment.

My aim is to investigate the effect of a convex and concave mirror on 4 rays of light.

My hypothesis is that when the light rays are reflected from the concave mirror, they will diverge inwards towards a focal point. When they are reflected from the convex mirror, they will diverge away and not form a focal point.

Apparatus & Materials:

  • Convex mirror
  • Concave mirror
  • Light box
  • Power box
  • Black slide with 4 slits.

Safety:

You must be careful to plug the light ray box into the power box and not into the wall socket because the the electricity can cause a serious electric shock and cause death.

Variables:

Independent variable: how the mirror bends.

Dependent variable: How the light rays react.

Controlled variables: amount of light rays

Method

1.Set up the power box

2.Plug in light box though the power box

3.Place the black slide in place

4.Place the concave mirror in front the light rays

5.Record observations and diagram

6.Place the convex mirror in front of the light rays

7.Record observations and diagram

8.Switch of power and unplug the light box

9.Allow the light box time to cool down before placing back into the box.

Results:

Diagram

Observations:

 Concave: The rays are reflected back towards the light box and are reflected with the ray reflecting towards the middle and converging at the focal point.

 Convex: The rays reflect outwards and do not have a focal point, they diverge. The 2 outside rays converge with the source rays on the outside. The focal point is virtual behind the mirror.

Discussion:

The reflected light rays diverge and do not meet at a focal point, this is because the mirror bends outwards and changes  the angle that the light rays reflect. The focal point of the light rays is virtual and would be located behind the mirror.

The concave mirror reflects the light rays towards each other and towards a focal point because the mirror curves inwards.

Evaluation:

I believe that the data is reliable but if we repeated the experiment using different mirrors and still use the same principle we would have improved the data, it would have shown that the hypothesis is not just for one type of mirror. A benefit of the method is that the light box allowed enough  light to show a clear image of what the lines were doing. Another benefit is that the  light box also allowed us to keep the  light equal, making the test fair.

An improvement I could have done is to repeat the experiment using different mirrors.  Another improvement could be to use different levels of light, this would have allowed us to prove that it doesn’t  matter what the light strength or type of mirror is used that  the hypothesis still works.

Conclusion:

In conclusion, my hypothesis ‘When the light rays are reflected from the concave mirror, they will diverge inwards towards a focal point. When they are reflected from the convex mirror, they will diverge away and not form a focal point.’ Is correct.

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