RP: Reflection + Refraction

What is Required Practical 9?

Investigate the reflection of light by different surfaces and refraction by different substances.

What apparatus is used to investigate reflection?

A ray box, plane mirror, paper, ruler and protractor.

How can the angle of incidence be measured?

Draw a normal at the point of incidence and measure the angle between the normal and incident ray.

How can the angle of reflection be measured?

Measure the angle between the normal and reflected ray.

Describe a method for investigating reflection.

Direct a narrow light ray at a plane mirror, mark the incident and reflected rays, draw the normal and measure both angles.

What relationship should be found between the angles of incidence and reflection?

They should be equal.

What is the independent variable in an investigation of reflection angles?

The angle of incidence.

What is the dependent variable in an investigation of reflection angles?

The angle of reflection.

Why should several different angles of incidence be tested?

To check whether the law of reflection holds across a range of angles.

What apparatus is used to investigate refraction?

A ray box, transparent block, paper, ruler and protractor.

Describe a method for investigating refraction through a glass block.

Trace the block, direct a narrow ray into it, mark the ray paths, draw the normals and measure the angles of incidence and refraction.

Why should the outline of the glass block be drawn?

To show the positions of the boundaries when the block is removed.

Why should a narrow beam of light be used?

To make the ray path easier to identify accurately.

Why must the glass block remain in the same position?

To avoid changing the ray path and measurement geometry.

What happens to light entering glass from air at an angle?

It usually bends towards the normal.

What happens to light leaving glass and entering air?

It usually bends away from the normal.

How can different substances be compared?

Pass light through different transparent materials at the same angle of incidence and compare the refraction.

What should be controlled when comparing refraction through different materials?

The angle of incidence, light source and measurement method.

Why should measurements be repeated?

To identify anomalies and improve reliability.

How can uncertainty in angle measurements be reduced?

Use thin, clearly marked rays and measure carefully with a protractor.

Why should the ray box be handled carefully?

Its lamp and casing may become hot during use.

What conclusion can be drawn from a refraction investigation?

Light changes direction when its speed changes at a boundary, except when travelling along the normal.