Question

a diffration grating has 250lines/cm. the 4th order image is formed at an angle of 4.00. what is the wavelength ?

Answer 1

the formula to use is wavelenth=dsin/n , but i am doing somthing wrong i thik

Answer 2

do we do simthing to 250?

Answer 3

We have 250 lines per cm. How many cm per line?

Answer 4

what u mean

Answer 5

d is the distance between lines.

If you have 250 lines per centimeter, what is the distance between the lines?

Answer 6

1/250?

Answer 7

Yep. Try using that for d, and you should be good to go!

Answer 8

i did that but still

Answer 9

is n 4 ?

Answer 10

If they are using the standard notation, yeah.

The center fringe is the 0th order, next out is 1st, etc.

Answer 11

the a answer is 698nm

Answer 12

what u did was 1/250*sin4/4

Answer 13

Remember, 1/250 is in cm.

Answer 14

so first its 1/250 * 1000?

Answer 15

what do we change it to ?

Answer 16

1/250 * 10^(-2) m

Answer 17

i still dont get 698nm

Answer 18

Strange. I do. Make sure your calculator is working with degrees (not radians)

\[\frac{1}{250} \times \sin(4^o) \times \frac{1}{4}\]

Answer 19

You should end up with 6.97565*10^(-07) m, which is (rounded to) 678 nm

Answer 20

oh okey i got that to before and i thought i was wrong

Answer 21

wait so how does that work ? how do u just round it ?

Answer 22

Ah
\[6.97565\times 10^{-7} = 697.565\times 10^{-9}\]

\[10^{-9}\textrm{m} = 1\textrm{nm}\]

Answer 23

so would it have been easier if i had converted 250cm to nm first?

Answer 24

just put 10^-9 after 250

Answer 25

1/250 cm to nanometers would have worked, yeah. "Easier" depends on how you look at it. I prefer to take everything to base units for situations like this.

Answer 26

No, not 10^(-9)

1/250 cm = 1/250 * 10^7 nm

Answer 27

You should look up a chart on metric conversions. Keep that around until you're more familiar with using it.

Answer 28

i have a chart

Answer 29

it says -9

Answer 30

10^(-9)m = nm
or
10^9 nm = m

nm are smaller, so there will be more of them.

Answer 31

can u help me with other questions

Answer 32

Sure

Answer 33

hold on

Answer 34

a photon with a wavelenth of 950nm has what frequecy

Answer 35

We know that
\[c = \lambda \nu \]
where c is the speed of light, lambda (the kind of h looking thing) is the wavelength, and nu (the v looking thing) is the frequency.

We know the speed of light is 3.0*10^8 m/s, so using the frequency, we can find the wavelength (be careful of units!!!)

Answer 36

the next question is the same but this time it says whats the energy ?

Answer 37

For a photon
\[E = h \nu\]
where h is Planck's constant

Answer 38

i have e=pc on my sheet

Answer 39

wait in the first question it was asked frequency their is no f in the equation u gave me

Answer 40

\[p = \frac{h}{\lambda} = \frac{h\nu}{c}\]
So
\[E = pc = \frac{h\nu}{c}c = h\nu\]

Answer 41

What you call c, I'm calling nu. I'll switch from here on out.

\[f = \nu\]

Answer 42

err, f. Not c.

Answer 43

oh ok

Answer 44

wait u mean no v but f

Answer 45

c is a constant and we need it