Snell's Law
A ray of light, travelling in air, passes into a glass block at an angle of 65° to the normal in air. The refractive index of glass is 1.5.
Calculate the angle of refraction.
37° to two significant figures (37.2°)
Explain what we mean by rays
Direction of wavefront
At which angle the ray refracts along the boundary
Critical angle
Why in physics we say 'blue bends best'
higher frequency deviate more than lower frequency
1 A ray of light, travelling in glass, passes through the glass–air boundary at an angle of 25° to the normal in the glass. The refractive index of glass is 1.5.
Calculate the angle of refraction.
39° to two significant figures (39.3°)
Explain what happens to the speed of light when it enters water
Slow down
What happens if the incident angle large than critical
Total internal reflection
Why diamonds sparkle?
has a very high refractive index, so separate the colours more than any other substance does.
1 A ray of light, travelling in air, passes into water. The angle of refraction is 23°. The refractive index of water is 1.33.
Calculate the angle of incidence.
31° to two significant figures (31.3°)
Explain what does not change when refraction occurs
Frequency
Name two conditions for total internal reflection
the incident substance has a larger refractive index
the angle of incidence exceeds the critical angle
Why does light bend when it passes from air into glass?
Light bends because it travels at different speeds in different media. When light enters a denser medium, such as glass, from a less dense medium, like air, it slows down. This change in speed causes the light to change direction, a phenomenon known as refraction. The extent of bending is determined by the refractive indices of the two media and follows Snell's Law.
1 The refractive index of acrylic glass is 1.49. The speed of light in air is approximately 3 ´ 108 ms−1.
Calculate the speed of light in acrylic glass.
2 x 108 ms−1
Explain the absolute refractive index
If medium 1 is a vacuum, the the refractive index for a ray travelling from the vacuum into a medium is a property of the medium called its absolute refractive index.
State the formula for the critical angle
sin theta c = 1/n1
Why does total internal reflection occur only when light travels from a denser to a less dense medium?
Total internal reflection occurs when light is moving from a denser medium (higher refractive index) to a less dense medium (lower refractive index) and strikes the boundary at an angle greater than the critical angle. At this angle, the refracted ray cannot pass into the less dense medium and is instead reflected entirely back into the denser medium. This phenomenon doesn't occur in the reverse direction because light bends towards the normal when entering a denser medium, rather than away from it.
A ray of light, travelling in liquid water, passes into an ice cube at an angle of 25.5° to the normal in water. The ray of light is refracted to an angle of 25.9° to the normal in the ice. The refractive index of liquid water is 1.33.
Calculate the refractive index of ice.
25.9° to three significant figures
Explain how the refractive index relates to the speed of light waves
speed of light in vacuum/speed in substance
state what n1 in the equation for critical angle means
the absolute refractive index of the material
Why do optical fibers rely on internal reflection to transmit light efficiently over long distances?
Optical fibers use total internal reflection to confine light within the core of the fiber. When light enters the fiber, it strikes the core-cladding boundary at angles greater than the critical angle, ensuring that it reflects internally without significant loss. This continuous reflection allows light signals to travel long distances with minimal attenuation, maintaining the signal's strength and integrity.