Critical Angle Experiment (Total Internal Reflection) - GCSE Required Practical

Summary

In this experiment, we explore how to find the critical angle of a semicircular perspex block using basic tools like a protractor, ruler, and pen. The video walks through the steps of tracing the block, marking the normal, and observing the refraction and total internal reflection at various angles. By determining the critical angle, which occurs just before total internal reflection, the refractive index of perspex is calculated using the formula. This experiment concludes with a refractive index of 1.5 for perspex, offering a hands-on understanding of light behavior through a transparent medium.

Takeaways

• 😀 The experiment aims to find the critical angle of a semicircular perspex block.
• 😀 Required materials include a pen, paper, ruler, protractor, Ray box, and a power source.
• 😀 The Ray box focuses light through a single slit aperture, producing a narrow beam.
• 😀 The perspex block is traced on the paper, with a boundary line and a normal drawn at a 90-degree angle to it.
• 😀 To find the critical angle, observe the ray transitioning from the denser medium (perspex) to the less dense medium (air).
• 😀 When the angle of incidence is smaller than the critical angle, light refracts into the air.
• 😀 When the angle of incidence equals the critical angle, the light travels along the boundary.
• 😀 If the angle of incidence exceeds the critical angle, total internal reflection occurs.
• 😀 The critical angle is found just before total internal reflection happens, and it's measured using a protractor.
• 😀 The refractive index of perspex is calculated using the equation: refractive index = 1 / sin(critical angle).
• 😀 Based on the critical angle of 43 degrees, the refractive index of perspex is calculated to be 1.5.

Q & A

What is the objective of this experiment?

The objective of the experiment is to find the critical angle of a semicircular perspex block.

What equipment is needed for this experiment?

You will need a pen and paper, ruler, protractor, and a ray box for this experiment.

How does the ray box contribute to the experiment?

The ray box focuses the light from the bulb and produces a narrow beam through the single slit aperture.

What is the purpose of the blanking plate in the experiment?

The blanking plate prevents light from leaking from the sides, ensuring the light beam remains narrow.

What is the significance of marking the 90-degree line on the perspex block?

The 90-degree line marks the normal, which is essential for measuring the angle of incidence and determining the critical angle.

What happens when the angle of incidence is smaller than the critical angle?

When the angle of incidence is smaller than the critical angle, the light is refracted into the air.

What occurs when the angle of incidence equals the critical angle?

When the angle of incidence is exactly equal to the critical angle, the light travels along the boundary between the perspex and air.

What phenomenon happens when the angle of incidence is larger than the critical angle?

When the angle of incidence becomes larger than the critical angle, total internal reflection occurs, and the light is fully reflected inside the perspex block.

How is the critical angle determined in the experiment?

The critical angle is found by marking the point just before total internal reflection, then measuring the angle between the incident ray and the normal using a protractor.

How can the refractive index of perspex be calculated from the critical angle?

The refractive index of perspex can be calculated using the formula: refractive index = 1 / sin(critical angle). For this experiment, the refractive index of perspex is 1.5.