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.

Two sound waves will 'cancel' each other 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 is produced by a laser directed at a double slit. Here are two statements about the central maximum of the interference pattern produced:

Which statements are true?

• A. None of them
• B. I
• C. II
• D. Both

5+6. 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 occurring at this point, compared to other points nearby.

5. 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. The microphone is moved to the centre position so that A, B and C are equal. it is then moved slowly to the left until a point of minimum amplitude is detected. At this point, A = 30cm, B = 28 cm and C = 32 cm.
The wavelength of the sound is therefore:

• A. 2 cm
• B. 4 cm
• C. 6 cm
• D. 8 cm

7-10: A green laser is directed at 2 narrow slits. A clear diffraction effect can be seen on a screen, with fringes as shown here:

7. 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'

8. 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?

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

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