Question 19

[mvenus9292913]

Where do you get P/4 from? I'm really confused...

You should know the equation for calculating tan?. tan? = opp/adj, and since l P/4 and L occupy the opposite and adjacent sides of the right triangle formed by their intersection with beam of light Y1 respectively, we may conclude tan? = (.5 P/4)/5 given the values provided for l and L. ? is then the arctan of (.5 P/4)/5 = tan-1[(.5 P/4)/5].

[admin]

Take a look at P/2 in Figure 1. The Center Line bisects P/2 into 2 segments where each is P/4.

Now let's consider a triangle where Y1 is the hypotenuse. You need to imagine (or draw on your scratch paper) line L (in other words, raise the L in the diagram so it touches Y1 on the far left side).

The angle formed between Y1 and L is theta2 (basic geometry). So far we have Y1 as the hypotenuse and L as the adjacent. Let's now see what is opposite:

There is l and P/4.

[zeina_ghou6141]

I still do not understand why P/4 is being added to l. Can you please clarify? Thanks!

[admin]

Try the directions above one more time (but take your time). If that does not work, let me know exactly what is not clear in the directions above.

The bottom line is that you have to imagine that Y1 is the hypotenuse of a triangle. If Y1 is the hypotenuse, then the side on the right is going to be l plus something. The geometry makes it necessary that that something is P/4.

[jgeng03]

I've read the above and I'm stuck at the point where I bring L up to the left side of Y1. I don't see what the relation between P and the triangle we drew or the smaller triangle on the right side with I as a side.

[admin]

If you have the diagram on paper, then examine the point where Y1 intersects the vertical line on the left. Now draw a horizontal line from that point of intersection to the vertical line on the right (the screen). The line you have drawn must be of length L.

Now consider the angle formed between Y1 and the line that you have just drawn. What is the length of the opposite side?

[ravichahal4519]

I see the relation ship between the 2 triangles but an still confused on the P/4.

am i to assume the distance P/2 is being divided in half when it intersects the bottom of the center line....

because if that's the case then i can see how the question works, all we are doing in enlarging the original triangle where we know the L, of 5m, still looking for the theta, but its an odd assumption to make is probably clone enough to get the approx answer

[jsfkt78927]

This question IMO is not answerable and requires a serious leap in logic and faith.

To look at a Figure which is "Not to Scale" and eyeball P/2 as being bisected by the center line is not logical. Besides, it doesn't even look like its bisecting it. I'd be willing to bet you an andrew jackson, that if you broke out the ruler and measured the top and bottom (on the left side of course), the bottom would be at least 50% further away from the center line.

[terryheidt1382]

This question took me 2 seconds to answer. The variable P was only in one answer choice and since the angle in question depends on the distance between the slit and the center line, 'D' was the only reasonable choice.