Light

Question 1

What type of wave is light, and what properties does it have?

Answer 1

• Light is a transverse wave.
• It can be reflected and refracted.

Question 2

What is the law of reflection?

Answer 2

• The angle of incidence equals the angle of reflection.
• This applies to all smooth reflective surfaces.

Question 3

What should be included in a ray diagram illustrating the reflection of light from a plane mirror?

Answer 3

• A normal line at the point of incidence.
• Show the incident ray and the reflected ray.
• Indicate the angles of incidence and reflection as equal.

Question 4

What should be included in a ray diagram illustrating the refraction of light through a glass block?

Answer 4

• Show a ray bending towards the normal when entering the block (denser medium).
• Show a ray bending away from the normal when exiting into air (less dense medium).
• Label angles of incidence, refraction, and emergence.

Question 5

Practical: How can you investigate the refraction of light using a rectangular glass block?

Answer 5

Method:
1. Place a rectangular glass block on a sheet of paper and trace its outline.
2. Shine a ray of light from a ray box at an angle into one side of the block.
3. Mark and draw the incident ray, refracted ray, and emergent ray.
4. Measure the angles of incidence and refraction using a protractor.
5. Repeat for multiple angles and record the values.
6. Analyze how the ray bends towards the normal when entering the glass and away when exiting.

Question 6

Practical: How can you investigate the refraction of light using a semi-circular block?

Answer 6

Method:
1. Place a semi-circular glass block on paper with the flat side facing the light source.
2. Shine a ray of light from the curved edge towards the flat surface.
3. Observe and record how the ray bends as it enters and exits the block.
4. Identify the critical angle where total internal reflection occurs.
5. Measure the angles of incidence and refraction.
6. Compare results with different angles to observe how refraction changes.

Question 7

Practical: How can you investigate the refraction of light using a triangular prism?

Answer 7

Method:
1. Place a triangular prism on white paper and trace its outline.
2. Shine a ray of light into one side of the prism at an angle.
3. Observe how the light bends twice (once entering and once exiting).
4. Identify the dispersion of light into a spectrum (if using white light).
5. Measure the angles of incidence, refraction, and emergence.
6. Compare different angles to study how light behaves in prisms.

Question 8

State and use the equation for refractive index.

Answer 8

n = sin(i) / sin(r)
- Where i = angle of incidence and r = angle of refraction.

Question 9

Practical: How can you determine the refractive index of glass using a glass block?

Answer 9

Method:
1. Place a rectangular glass block on a sheet of paper and trace its outline.
2. Shine a ray of light from a ray box at an angle into one side of the block.
3. Mark and draw the incident, refracted, and emergent rays.
4. Measure angles i and r using a protractor.
5. Use the formula n = sin(i) / sin(r) to calculate the refractive index.
6. Repeat with different angles for improved accuracy.

Question 10

Define total internal reflection and state when it occurs.

Answer 10

• Total internal reflection occurs when light is completely reflected inside a medium instead of refracting.
• It happens when the angle of incidence is greater than the critical angle.
• Used in optical fibres and prisms for efficient light transmission.

Question 11

Explain how total internal reflection enables optical fibre communication.

Answer 11

• Light enters an optical fibre at an angle greater than the critical angle.
• The light is reflected repeatedly inside the fibre due to total internal reflection.
• No significant loss of energy occurs, enabling fast and secure data transmission.
• Used in medical endoscopes and high-speed internet cables.

Question 12

Define the critical angle and explain its significance.

Answer 12

• The critical angle is the minimum angle of incidence at which light is refracted exactly along the boundary of a medium.
• Beyond this angle, total internal reflection occurs.

Question 13

State and use the equation for the critical angle in relation to refractive index.

Answer 13

sin(c) = 1 / n
- Where c = critical angle, n = refractive index.