1) When a single source of light shines through an extremely thin rectangular sl

Question

1) When a single source of light shines through an extremely thin rectangular slit and projects on a far away viewing screen, a single rectangular region of the viewing screen is illuminated (matching the shape of the thin rectangular slit).

True or False?

2) Which (one or more) of the following choices ALWAYS describes two separate light waves that are in phase at a single location?

Both light waves have the same intensity at that location at one instant in time.

Both light waves have a peak (their most positive electric and magnetic fields) at that location at one instant in time.

Both light waves have a trough (their most negative electric and magnetic fields) at that location at one instant in time.

Both light waves are at their equilibrium states (no electric or magnetic fields) at that location at one instant in time

3) When a single source of light shines through an extremely thin rectangular slit and projects on a far away viewing screen, a single rectangular region of the viewing screen is illuminated (matching the shape of the thin rectangular slit).

True or False?

Both light waves have the same intensity at that location at one instant in time.

Both light waves have a peak (their most positive electric and magnetic fields) at that location at one instant in time.

Both light waves have a trough (their most negative electric and magnetic fields) at that location at one instant in time.

Both light waves are at their equilibrium states (no electric or magnetic fields) at that location at one instant in time

Explanation / Answer

1. False.

If the width of the slit is small enough that it is comparable to the wavelength of the light source, diffraction of light can be observed and we observe fringes on the screen. with a bright central fringe and successively darker fringes.

2. The waves are said to be 'in phase'. This implies that they are of the same frequency.

a) We know nothing of the intensities of the individual light waves. So, this is not necessarily true.They always have 0 intensities at the same time but other than that, we cannot say anything else

b) The waves are in phase. Therefore, thesinusoidal part of the wave is the same. Therefore, both have electric and magnetic fields maximum. ie, the sinusoidal part being 1, at the same time. So, true

c) SImilar to the above, since both have same sinusoidal part, the sinusoidal part will be -1 at the same time/. SO, true

d)SImilar to the above, since both have same sinusoidal part, the sinusoidal part will be 0 at the same time. So, true

3 I don't see how this is different from problem 1

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