Understanding Light Refraction Laws
When light travels from one transparent medium to another (like from air to water), it changes direction. This bending of light is known as refraction. The path light takes is not random; it follows specific rules described by the laws of refraction.
Key Terms Explained
- Incident Ray: This is the initial ray of light approaching the surface that separates the two different media.
- Point of Incidence: This is the exact spot on the surface where the incident ray makes contact.
- Refracted Ray: After passing through the surface and entering the second medium, the ray of light continues as the refracted ray.
- Normal: This is an imaginary line drawn perpendicular to the surface at the point of incidence. It serves as a reference line to measure angles. A perpendicular line forms a $90^{\circ}$ angle with the surface.
The Laws Governing Refraction
The behavior of light during refraction is precisely defined by two fundamental laws:
- The Plane Law: The incident ray, the refracted ray, and the normal, all drawn at the point of incidence, must lie together in the same plane.
- Snell's Law: This law relates the angles of incidence and refraction to the properties of the two media. It states that the ratio of the sine of the angle of incidence ($\theta_i$) to the sine of the angle of refraction ($\theta_r$) is constant for a given pair of media and a specific wavelength of light. Mathematically, this is expressed as: $ \frac{\sin(\theta_i)}{\sin(\theta_r)} = n $ where '$n$' represents the refractive index, a measure of how much light slows down and bends in a medium.
Analyzing the Given Statements
Let's evaluate each option based on the laws of refraction:
Option 1: The normal is always at a $90^{\circ}$ angle to the refracted ray.
This statement is incorrect. The normal is defined as being at a $90^{\circ}$ angle to the *surface* at the point of incidence. The angle between the normal and the refracted ray is called the angle of refraction ($\theta_r$), which can vary and is generally not $90^{\circ}$.
Option 2: The incident ray, the refracted ray, and the normal all lie in the same plane at the point of incidence.
This statement is correct. It accurately describes the first law of refraction, which dictates that these three components (incident ray, refracted ray, and normal) are coplanar at the point where light enters the new medium.
Option 3: Only the incident and refracted rays lie in the same plane, excluding the normal.
This statement is incorrect. As per the first law of refraction, the normal must also be included in the same plane along with the incident and refracted rays.
Option 4: They all travel in different directions randomly.
This statement is incorrect. Light refraction is a predictable phenomenon governed by physical laws. The directions of the incident ray, refracted ray, and normal are not random but follow precise mathematical relationships.
Important Questions from Basic Concepts in Physics
- What happens when the vibration of a sound source becomes faster?
$50 \ \Omega$, $50 \ \Omega$ and $100 \ \Omega$ resistors are connected in series in a circuit. They can be replaced with a single resistor of ______________in the circuit.
- Work done by a force on a body is said to be negative when:
- What is the value of the force exerted by the Earth on a satellite, if the mass of the Earth is $6 \times 10^{24}$ kg and the mass of the satellite is 400 kg. The satellite is orbiting the Earth at a distance of 400 km from its surface. The radius of the Earth is 6400 km and G = $6.67 \times 10^{-11}$ N m$^2$/kg$^2$.
- A person with eye defect of ___________ cannot see nearby objects distinctly, which is corrected using a ___________ lens of suitable power.
