 µ IB | Interference

10 quick questions

10 minutes maximum! (can you do it in 5?)

1. What is the name given to the addition of waves when they meet at a point?

• A. Summation of waves.
• B. Superposition of waves.
• C. Vector analysis of waves.
• D. Total internal effect of waves.

2. Waves produce clear interference patterns when they are 'coherent'. This means the waves....

• A. have the same amplitude.
• B. have a constant phase difference.
• C. have the same velocity.
• D. are always in phase.

3. Noise cancelling headphones work by using the effect of interference. Two sound waves will 'cancel' eachother out if they ...

• A. are in phase.
• B. have ½ π radians phase difference.
• C. have π radians phase difference.
• D. have 2π radians phase difference. 4. An interference pattern can be produced by a single slit and a double slit. On the right are two statements about the central maximum of the interference pattern produced.

These two statements are both true for:

• A. Single slit intererference only.
• B. Double slit intererference only.
• C. Both double and single slit interference.
• D. Neither double aor single slit interference.

I The central maximum is always caused by constructive intereference.

II The central maximum is twice as wide as the other peaks in the pattern.

5. A microphone is placed in front of two loudspeakers as shown here. The amplitude of the sound detected is very high, indicating that constructive interference is occuring at this point, compared to other points nearby. What condition is needed for constructive interference at this point?

• A. The distance A is an exact multiple of the wavelength of the sound.
• B. The distance (B-C) is an exact multiple of the wavelength of the sound.
• C. The distance (B+C) is an exact multiple of the wavelength of the sound.
• D. The distance (B+C) is equal to half of the wavelength of the sound.

6-9: A green laser is directed at 2 narrow slits. A clear diffraction effect can be seen on a screen, with fringes as shown here: 6. The formula on the right is used for double slit diffraction. Which letter/symbol in the formula represents the distance between fringes?

• A. ' s'
• B. 'λ'
• C. 'D'
• D. 'd' 7. What happens to the intensity of the fringes, and the distance between fringes if the green laser is replaced with a red laser of equal power output?

 Intensity of fringes distance between fringes A stays the same increases B stays the same decreases C increases stays the same D decreases stays the same

8. What happens if the green laser remains but the distance between the 2 slits is decreased?

 Intensity of fringes distance between fringes A stays the same increases B stays the same decreases C decreases increases D decreases decreases

9. What happens if the green laser remains, the spacing between slits stays constant but each of the slit widths is decreased?

 Intensity of fringes distance between fringes A stays the same increases B stays the same decreases C decreases increases D decreases stays the same

10. A single slit can produce a diffraction pattern with light and dark bands. What produces this pattern?

• A. Interference between light of different frequencies from the slit.
• B. Interference between light originating from different points within the slit.
• C. Interference between light from the slit and light from external sources.
• D. Interference between light from the slit and reflected light from the screen.