To Study the Laws of Reflection (Class 9 Physics Practical)
To verify the laws of reflection using a plane mirror, a light ray, and measurement of angles.
TL;DR: To verify the laws of reflection using a plane mirror, a light ray, and measurement of angles.
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Aim: To verify the laws of reflection using a plane mirror, a light ray, and measurement of angles.
Materials Required
- Wooden board
- Plane mirror
- Pins (4-5)
- Protractor
- Meter scale
- Paper
- Pencil
Theory
The laws of reflection state that: (1) the incident ray, reflected ray, and normal all lie in the same plane, and (2) the angle of incidence equals the angle of reflection. These angles are measured from the normal to the mirror surface.
Procedure
- Draw a line on the paper to represent the mirror and a perpendicular line (normal) to it
- Place the mirror on the drawn line and secure it
- Draw an incident ray towards the mirror at an angle
- Place two pins along the incident ray and observe their reflections in the mirror
- Place two more pins such that they are aligned with the reflected image of the first two pins
- Draw the reflected ray along these pins
- Measure the angle between the incident ray and the normal (angle of incidence)
- Measure the angle between the reflected ray and the normal (angle of reflection)
- Repeat with different angles of incidence and record all observations
Observation
For all incidents rays at different angles, the reflected ray is clearly visible in the mirror. The angle of incidence and angle of reflection are found to be equal in each case. Both rays lie in the plane of the paper (same plane as the normal).
Result
The laws of reflection are verified. The angle of incidence equals the angle of reflection for all test cases, confirming that light reflects at equal angles.
Precautions
- Keep the mirror perpendicular to the board
- Mark the normal perpendicular to the mirror accurately
- Use sharp pins and observe from directly above
- Measure angles from the normal, not from the mirror surface
- Ensure the pins are aligned properly before drawing the rays
Viva Questions
State the laws of reflection.
The laws of reflection state that the angle of incidence equals the angle of reflection, and both rays lie in the plane containing the normal.
Why must we draw a normal to the mirror?
The normal is the reference line from which angles of incidence and reflection are measured.
Can reflection occur without the incident and reflected rays being in the same plane?
No, the incident ray, reflected ray, and normal must always lie in the same plane.
What is the angle of incidence for a ray hitting the mirror perpendicularly?
The angle of incidence is zero when the ray is perpendicular to the mirror, and the ray reflects straight back.
More Class 9 Physics Practicals
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- To Verify Ohm's Law
- To Find Resistance Using a Metre Bridge
- To Determine the Density of a Solid
- To Verify the Laws of Refraction (Glass Slab)
- To Study a Simple Pendulum and Find the Acceleration Due to Gravity (g)
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