Reflection, refraction and diffraction of waves

Answer Key - Grade 11 Science Worksheet - Challenge Me

Circle the best answer, or write your answer on the line.

1. 1.

   A ray in air hits a clear liquid at 45° from the normal and refracts at 30° from the normal. What is the liquid's refractive index, to 2 decimals, Ari?

   1.41 n
2. 2.

   A ray in air hits a clear liquid at 60° from the normal and refracts at 40° from the normal. What is the liquid's refractive index, to 2 decimals, Bo?

   1.35 n
3. 3.

   A ray in air hits a clear liquid at 70° from the normal and refracts at 38° from the normal. What is the liquid's refractive index, to 2 decimals, Esme?

   1.53 n
5. 4.

   The table was taken with a 2.0 cm wavelength. What does it show about the gap, Jun?

   • Narrowing the gap toward the wavelength spreads the waves more, up to 90° at 2.0 cm
   • The spread depends on the size of the gap alone, not on the wavelength, as this table shows
   • A gap narrower than 2.0 cm stops the waves completely, so there is no angle for it
   • Widening the gap toward the wavelength spreads the waves more, as the angle column shows
6. 5.

   Kira doubles the ripple frequency in the same tank, so the wavelength halves. What is the first-minimum angle for the 4.0 cm gap now?

   Use the picture in question 4.

   • 7°, since halving the wavelength halves the angle
   • 60°, since doubling the frequency doubles the angle
   • 14°, the same as the 8.0 cm gap gave before
   • 30°, the same as before, since the gap has not changed
7. 6.

   A doorway 0.9 m wide casts a sharp light shadow. Milo says light does not diffract. Light's wavelength is 500 nm. Agree or disagree?

   • Agree: light diffracts through gaps narrower than the doorway, and this one is not narrow enough
   • Disagree: light does diffract, but 500 nm is about two million times smaller than the doorway
   • Agree: a sharp shadow means light travels in straight lines, so it cannot diffract, whatever the gap
   • Disagree: light spreads a lot, but the spread is hidden by the brightness of the room
8. 7.

   In one glass, n is 1.51 for red light and 1.53 for violet. Noah says red bends most on entering the glass, since it has the longest wavelength. Agree or disagree?

   • Agree: red is slower in glass because its frequency is lower than violet's
   • Disagree: violet slows down more in the glass, so it bends more toward the normal
   • Disagree: red and violet bend the same amount, because n is almost equal
   • Agree: the longest wavelength means the largest change when light enters the glass
9. 8.

   Pia says the angle in the liquid is always the same fraction of the angle in air. Does the table support the claim?

   • Yes: the angle in the liquid rises as the angle in air rises
   • No: the angles rise by the same step each time, so they cannot be a fraction
   • Yes: the angle ratio is 0.75 at 20° and about the same at 60°
   • No: the angle ratio falls from 0.75 to 0.67, while the sine ratio stays near 1.33
10. 9.

    An ultrasound scanner must show details as small as 0.25 mm, so the wavelength must be no more than that. Sound in soft tissue travels at about 1540 m/s. What frequency is needed, Tala?

    • At least about 0.62 MHz
    • At least about 3.1 MHz
    • At least about 6.2 MHz
    • At least about 62 MHz
11. 10.

    A depth sounder assumes 1481 m/s, but sound in this seawater travels at 1500 m/s. An echo returns after 0.120 s. What does it read, and how far off is it, Zee?

    • It reads 177.7 m, which is 2.3 m too shallow
    • It reads 88.9 m, which is 1.1 m too shallow
    • It reads 88.9 m, which is 1.1 m too deep
    • It reads 90.0 m, which is correct