Physics

A laser produces light of wavelength lambda. The light is directed through two splits that are separated by a small distance. On the other side of the slits is an interference pattern of alternating dark(black) and bright bands. What is the wavelength of the light in the bright bands?
2lambda
Lambda
0.5 lambda
9 lambda
A train passes a farm house at 30.0 m/s and then the engineer sounds the 900-Hz whistle. The air is still and the speed of sound is 340 m/s. What frequency will a person inside the farmhouse hear? Assume that the angle between the farmhouse and the train is negligible.
883 Hz
827 Hz
877 hz(my choice)
871 Hz
You are 15.0 m from the source of a sound. At that distance, you hear it at a sound level of 20.0 dB. How close must you move to the sound to increase the sound level to 60 dB?
15.0 cm
45.0 cm
55.0 cm
60.0 cm
85.0 cm
Please help. I’ll really appreciate it.

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  1. The interference pattern does not change the wavelength of the light ! Either this is a typo or the answer is lambda.

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  2. google doppler shift
    340/370 * 900 = 827

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  3. logs are base 10

    change in dB = 10 log P2/P1
    40 = 10 log P2/P1
    log P2/P1 = 4
    P2/P1 = 10^4
    the power goes square of distance inverted (same power through 4pi r^2)
    distance ratio = 10^2 = 100
    .15 meter = 15 cm

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