Refraction of Light

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Questions and Answers

Under what condition does a light ray not change its direction when refracting?

  • When light enters from a denser to a rarer medium
  • When the angle of incidence at the boundary is zero (correct)
  • When the refractive index of both media is different
  • When the angle of incidence is 90°

What happens to the speed of light when it moves from a rarer medium to a denser medium?

  • It remains constant
  • It decreases (correct)
  • It becomes equal to the speed of sound
  • It increases

Which of the following factors does NOT affect the refractive index of a medium?

  • Nature of the medium
  • Temperature
  • Speed of light in a vacuum (correct)
  • Color of light

In which scenario does the wavelength of light change during refraction?

<p>When light passes from a rarer to a denser medium (D)</p> Signup and view all the answers

Which color of light travels the slowest in a medium?

<p>Violet light (A)</p> Signup and view all the answers

What does the principle of reversibility of light state?

<p>The path of a light ray is reversible (B)</p> Signup and view all the answers

How does increasing temperature in a medium affect its refractive index?

<p>It decreases the refractive index (D)</p> Signup and view all the answers

What remains unchanged during the process of refraction of light?

<p>Frequency of light (D)</p> Signup and view all the answers

What happens to a light ray as it enters a glass block from air?

<p>It bends towards the surface normal. (B)</p> Signup and view all the answers

What is the relationship between the angle of incidence and the angle of emergence in a rectangular glass block?

<p>They are always equal. (B)</p> Signup and view all the answers

What is the lateral displacement of a light ray as it passes through a glass block?

<p>The distance between the incident and emergent rays. (B)</p> Signup and view all the answers

What type of medium is a prism classified as?

<p>A five-sided transparent medium. (D)</p> Signup and view all the answers

In terms of refraction, which equation relates the refractive indices and sine of the angles?

<p>$\mu_1 \sin i = \mu_2 \sin r$ (B)</p> Signup and view all the answers

What describes the path of a light ray after passing through a rectangular glass block?

<p>It continues parallel to the incident ray. (B)</p> Signup and view all the answers

What can be concluded about the normal line in relation to the surfaces of a glass block?

<p>The normal is always perpendicular to the rays. (A)</p> Signup and view all the answers

What characteristic does a prism have concerning its geometry?

<p>It possesses two triangular bases. (C)</p> Signup and view all the answers

What is the term used for the angle between the two refracting surfaces of a prism?

<p>Angle of prism (B)</p> Signup and view all the answers

What happens to a monochromatic ray of light when it strikes the face AB of a prism?

<p>It suffers refraction and travels along PQ (A)</p> Signup and view all the answers

In the context of a prism, what is the emergent ray represented as?

<p>QR (C)</p> Signup and view all the answers

Which of the following equations represents the relationship between the angle of incidence, angle of emergence, and angle of deviation?

<p>i1 + i2 = A + δ (A)</p> Signup and view all the answers

What does the angle of deviation (δ) depend on?

<p>The angle of prism and color of light used (A)</p> Signup and view all the answers

How is the angle of incidence at face AC denoted?

<p>i2 (D)</p> Signup and view all the answers

When viewed from a rarer medium, where does an object in a denser medium appear to be?

<p>At a lesser depth (B)</p> Signup and view all the answers

What is the principal section of the prism?

<p>The section perpendicular to the refracting edge (A)</p> Signup and view all the answers

What occurs when light travels from a rarer medium to a denser medium?

<p>It bends towards the normal. (B)</p> Signup and view all the answers

What is the deviation of the ray when it travels from a denser medium to a rarer medium?

<p>The deviation is the difference between the angles of refraction and incidence. (D)</p> Signup and view all the answers

According to Snell's law, what remains constant for a given pair of media?

<p>The ratio of the sine of the angle of incidence to the sine of the angle of refraction. (D)</p> Signup and view all the answers

What is the absolute refractive index of a transparent medium with respect to vacuum?

<p>It is always greater than 1. (B)</p> Signup and view all the answers

What happens to a ray of light incident normally on the surface separating two media?

<p>It passes undeviated. (C)</p> Signup and view all the answers

What happens to the critical angle when the temperature of a medium increases?

<p>It increases. (D)</p> Signup and view all the answers

Which color of light has the lowest refractive index when passing through a medium?

<p>Red (D)</p> Signup and view all the answers

What is the formula for the refractive index of medium 2 with respect to medium 1?

<p>$1 , ext{n}_2 = \frac{v_1}{v_2}$ (A)</p> Signup and view all the answers

When light moves from a denser medium to a rarer one, which of the following statements is true?

<p>The angle of incidence is less than the angle of refraction. (C)</p> Signup and view all the answers

Under what condition does total internal reflection occur?

<p>When light travels from a denser medium to a rarer medium at an angle greater than the critical angle. (C)</p> Signup and view all the answers

How does the brightness of an image formed by total internal reflection compare to that of a reflection from a plane mirror?

<p>It is brighter and permanent. (D)</p> Signup and view all the answers

How fast does light travel in vacuum?

<p>$3 \times 10^8 , \text{m/s}$ (D)</p> Signup and view all the answers

What is the relationship between critical angle and wavelength of light?

<p>Critical angle increases with increasing wavelength. (D)</p> Signup and view all the answers

What is the relationship between the angle of incidence and the angle of refraction when light travels from a denser medium to a rarer medium?

<p>Angle of incidence is greater than angle of refraction. (A)</p> Signup and view all the answers

What happens to the apparent depth of an object when viewed in water compared to its real depth?

<p>The apparent depth is less than the real depth. (C)</p> Signup and view all the answers

What is the impact on light energy during total internal reflection?

<p>There is no loss of energy. (D)</p> Signup and view all the answers

What is the critical angle?

<p>The angle of incidence causing total internal reflection. (B)</p> Signup and view all the answers

What defines the refractive index of a medium with respect to glass?

<p>It is always greater than 1. (A)</p> Signup and view all the answers

Which of the following best describes why we see the sun before it actually rises?

<p>Because of the bending of light rays in the atmosphere. (A)</p> Signup and view all the answers

What occurs at the boundary of a plane mirror when light is incident?

<p>Light is reflected at any angle of incidence. (D)</p> Signup and view all the answers

How is the shift between real depth and apparent depth calculated?

<p>Shift = Real depth - Apparent depth (D)</p> Signup and view all the answers

In which scenario does a star appear to twinkle?

<p>Because of the Earth's atmosphere affecting starlight. (D)</p> Signup and view all the answers

When the angle of incidence is equal to the critical angle, what happens to the light ray?

<p>It reflects back into the denser medium. (A)</p> Signup and view all the answers

What phenomenon occurs when a coin at the bottom of a vessel becomes visible after pouring water into it?

<p>Refraction caused by the water. (C)</p> Signup and view all the answers

Flashcards

Refraction of Light

The bending of light as it passes from one transparent medium to another.

Snell's Law

The ratio of the sine of the angle of incidence to the sine of the angle of refraction, constant for a given pair of media and wavelength.

Refractive Index (n)

The ratio of the speed of light in vacuum to the speed of light in a given medium.

Ray of Light Bending (Denser)

When a ray of light travels from a rarer medium to a denser medium, it bends towards the normal.

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Ray of Light Bending (Rarer)

When a ray of light travels from a denser medium to a rarer medium, it bends away from the normal.

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First Law of Refraction

The incident ray, refracted ray, and normal at the point of incidence all lie in the same plane.

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Speed of Light in Vacuum

The speed of light in a vacuum, the fastest it can travel.

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Absolute Refractive Index

The absolute refractive index of a medium is always greater than 1.

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Refracting Surfaces

The two rectangular surfaces of a prism through which light enters and exits. Their angle determines the prism's shape.

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Angle of Prism

The angle formed by the intersection of the two refracting surfaces.

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Refracting Edge

The line where the two refracting surfaces meet, perpendicular to the principal section.

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Principal Section

The cross-section of the prism perpendicular to the refracting edge, showing its shape.

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Base of the Prism

The surface opposite the refracting edge, forming the base of the prism's shape.

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Angle of Deviation

The angle between the direction of the incident ray and the emergent ray.

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Deviation at Each Surface

The difference between the angle of incidence and the angle of refraction at each surface.

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Apparent Depth

The apparent depth of an object submerged in a denser medium is shallower than its actual depth when viewed from a rarer medium due to refraction.

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Refractive Index Relation

The ratio of the refractive index of medium 1 to the refractive index of medium 2 is equal to the ratio of the speed of light in medium 2 to the speed of light in medium 1.

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Rectangular Glass Block

A rectangular block of transparent material, usually glass, with parallel opposite faces.

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Lateral Displacement

When a ray of light passes through a parallel-sided glass block, the emergent ray is parallel to the incident ray, but laterally displaced.

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Prism

A transparent refracting medium bounded by five plane surfaces inclined at some angles.

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Angle of Incidence

The angle between the incident ray and the normal to the surface at the point of incidence.

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Angle of Refraction

The angle between the refracted ray and the normal to the surface at the point of refraction.

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Angle of Emergence

The angle between the emergent ray and the normal to the surface at the point of emergence.

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What is refraction?

When light passes from one medium to another, it changes direction. This bending of light is called refraction.

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When does refraction NOT occur?

The angle of incidence is 0 degrees when the light ray hits the boundary perpendicularly. This means the light ray doesn't bend.

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What causes light to refract?

The speed of light changes as it moves from one medium to another. This change in speed is what causes the light to bend.

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What is the refractive index?

The refractive index of a medium describes how much light bends when it enters that medium. It's a measure of how much the speed of light slows down in that medium compared to air.

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How is refractive index related to the speed of light?

The refractive index of a medium is higher if the speed of light is lower in that medium. For example, water has a higher refractive index than air because light travels slower in water.

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How does temperature affect refractive index?

The refractive index of a medium changes depending on the medium's temperature. As the temperature increases, the particles in the medium move faster, allowing light to travel faster and reducing the refractive index.

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What is the principle of reversibility of light?

The principle of reversibility means that if a light ray travels from medium 1 to medium 2, it would follow the same path in reverse if it traveled from medium 2 to medium 1.

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What happens to frequency and wavelength during refraction?

The frequency of light (which determines its color) remains constant even when it travels from one medium to another. However, because its speed changes, its wavelength also changes.

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Refractive Index

The ratio of the sine of the angle of incidence to the sine of the angle of refraction, which represents how much a light ray bends when passing from one medium to another.

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Shift

The difference between the real depth of an object and its apparent depth when submerged in a medium.

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Critical Angle

The angle of incidence in the denser medium at which the angle of refraction in the rarer medium is 90 degrees. Beyond this angle, the light ray undergoes total internal reflection.

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Total Internal Reflection

The phenomenon where light rays traveling from a denser medium to a rarer medium are reflected back into the denser medium when the angle of incidence exceeds the critical angle. This is the reason why diamonds sparkle.

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Refractive index of air with respect to glass

The refractive index of air with respect to glass can be calculated using the sine of the angle of incidence in air and the sine of the angle of refraction in glass.

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Critical angle and wavelength

The critical angle increases as the wavelength of light increases. Violet light has the smallest critical angle, while red light has the largest.

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Critical angle and temperature

As the temperature of a medium increases, its refractive index decreases, leading to a larger critical angle for that pair of media.

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Reflection from a plane mirror

Reflection of light from a smooth surface, where all the light rays are reflected in a single direction.

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Diffuse reflection

Reflection of light from a rough surface, where the light rays are scattered in multiple directions.

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Study Notes

Refraction of Light

  • Refraction is the change in direction of light as it passes from one transparent medium to another.
  • This is a surface phenomenon.
  • When light goes from a rarer medium to a denser medium, it bends towards the normal. The deviation is (i − r). (i= angle of incidence, r= angle of refraction)
  • When light goes from a denser medium to a rarer medium, it bends away from the normal. The deviation is (r − i).
  • A ray of light incident normally on a surface passes undeviated.
  • Light bends because its speed changes.

Laws of Refraction

  • The incident ray, refracted ray and the normal to the surface all lie in the same plane.
  • The ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant for a given pair of media and for a given wavelength. This is Snell's Law. (sin i / sin r = constant = μ₂/μ₁) (μ=refractive index)

Speed of Light and Refractive Index

  • Light travels fastest in a vacuum (c = 3 × 10⁸ m/s).
  • The refractive index of medium 2 with respect to medium 1 (μ₂₁) is the ratio of the speed of light in medium 1 to the speed of light in medium 2 (v₁/v₂).
  • The refractive index of a medium is always greater than 1.

Change in Speed, Direction and Wavelength of Light

  • Light's speed changes during refraction.
  • Light bends when passing between media with different densities
  • Frequency of light does not change during refraction
  • Wavelength changes due to the change in the speed of light

Factors affecting Refractive Index

  • Optical density of the medium. A medium with a higher optical density has a greater refractive index.
  • Temperature—higher temperatures increase the speed of light in a medium, reducing the refractive index.
  • Colour/wavelength—the speed of different colours of light is different in a medium. Violet has a higher refractive index, while red has a lower refractive index.

Principle of Reversibility of the Path of Light

  • The path of a light ray undergoing refraction is reversible.

Refraction through a Rectangular Glass Block

  • Light bends towards the normal when passing from air to glass.
  • Light bends away from the normal when passing from glass to air.
  • The emergent ray is parallel to the incident ray, but not in the same line—there is a lateral displacement.

Prism

  • A prism is a transparent medium with a triangular cross-section.
  • The angle between the two refracting surfaces is the angle of prism.
  • The intersection line is the refracting edge.
  • Refraction of light through a prism causes deviation.
  • Deviation depends on the angle of incidence, the refractive index of the prism, and the angle of the prism.

Total Internal Reflection

  • Total internal reflection occurs when light going from a denser to a rarer medium, at an angle greater than the critical angle.
  • The ray is completely reflected back into the denser medium.

Critical Angle and Refractive Index

  • The critical angle is the incident angle in denser medium, where the refracted angle in the rarer medium is 90°.
  • The critical angle depends on the refractive index. (sin ic = 1/μ₂)

Real Depth and Apparent Depth

  • Real depth is the actual distance of an object from the surface.
  • Apparent depth is the perceived distance of the object from the surface.
  • When viewed through a medium (like water), the object appears closer to the surface than its actual position.
  • (Apparent depth/Real depth = n₂)

Consequences of Refraction of Light

  • Stars twinkle due to atmospheric refraction; starlight bends multiple times.
  • The apparent position of stars differs.
  • The Sun appears a few minutes before sunrise and after sunset due to atmospheric refraction.

Optical fibres

  • Used for transmitting light (and consequently data) over long distances with relatively low signal loss.

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