## Speed of light

$c=\lambda v$

Emily_Stenzler_2H
Posts: 196
Joined: Wed Sep 30, 2020 10:02 pm

### Speed of light

I have been using 3.00*10^8 for the speed of light, but I noticed the textbook uses 2.998*10^8. I was thinking this would be determined based on sig figs but the question I'm looking at in the textbook (example 1A.1) has 2 sig figs for the numbers in the question. How do we know which to use? It sounds like grading may be a bit picky and I know these two values would lead to different answers, even though they vary by a small amount. Please let me know :)

Quinton Sprague 1A
Posts: 97
Joined: Wed Sep 30, 2020 9:35 pm

### Re: Speed of light

Hello,
The value 2.998 x 10^8 m/s is the most precise so although it is easy to remember 3.0 x 10^8, if the grading is very picky, it is likely best to go with the figure closest to its exact value, that being the 2.998 x 10^8 representation of the speed of light.

Kaley Qin 1F
Posts: 92
Joined: Wed Sep 30, 2020 9:54 pm

### Re: Speed of light

For tests, Lavelle said that for constants, he will give you the exact value he wants you to use so there will be no discrepancies between students.

Lorraine Medina 3E
Posts: 125
Joined: Wed Sep 30, 2020 10:11 pm

### Re: Speed of light

Dr. Lavelle has an equation sheet for the tests, so I would use whatever number is on that sheet for the midterm/final.

Veronica Macias 3K
Posts: 77
Joined: Wed Sep 30, 2020 9:36 pm
Been upvoted: 1 time

### Re: Speed of light

Lorraine Medina 3C wrote:Dr. Lavelle has an equation sheet for the tests, so I would use whatever number is on that sheet for the midterm/final.

Dr. Lavelle has an equation sheet on his website already titled "Constants and Equations." This will probably be the sheet we are given on the midterms and final. The value for c on there is 2.99792 x 10^8 m.s^-1. I have been using the numbers for the constants on this equation sheet for problems and they have been giving me the right answers.

t_rasul2I
Posts: 98
Joined: Wed Sep 30, 2020 9:38 pm

### Re: Speed of light

I think for the midterm, since it is multiple choice, we can use either value to calculate because we should still get a very close answer to the correct answer.

505598869
Posts: 88
Joined: Wed Sep 30, 2020 9:43 pm

### Re: Speed of light

I would use whatever numbers Dr. Lavelle gives us on his constants/equations sheet.

Anya Holbrook 1E
Posts: 92
Joined: Wed Sep 30, 2020 9:38 pm

### Re: Speed of light

I've been using 2.998 x 10^8 rather than 3.00 x 10^8, and just rounding my final answer to the correct number of sigfigs, and it seems to have been working so far!

Jessica Hu 3L
Posts: 51
Joined: Wed Sep 30, 2020 9:46 pm

### Re: Speed of light

Regardless of the precise constant you use, the test is multiple choice, therefore your answer should be close enough to one of the options given.

Morgan Gee 3B
Posts: 95
Joined: Wed Sep 30, 2020 9:48 pm

### Re: Speed of light

Because our midterm is going to be multiple choice, it probably does not matter too much how many significant figures you use. However, I personally plan on using as many as possible to be as accurate as possible.

Aria Movassaghi 1A
Posts: 97
Joined: Wed Sep 30, 2020 9:40 pm

### Re: Speed of light

In the past I've used 3.00 but now I just use the constants that are on the provided page by Dr. Lavelle. However it should not make a big difference on a multiple choice exam.

Joshua Chung 2D
Posts: 96
Joined: Wed Sep 30, 2020 9:32 pm

### Re: Speed of light

Though 3.0 will probably be fine in most questions, you can round to math the sig figs of the given values just to be safe.

SophiaBarden 2E
Posts: 94
Joined: Wed Sep 30, 2020 10:07 pm

### Re: Speed of light

From friends that have taken Lavelle's classes before; The sig figs matter! Lavelle will give you options that give the same answer but with varying sigfigs to test your knowledge (and rounding ability for some reason lol). So make sure you use the exact values given on the constants and equations sheet, and note the sig figs for those numbers.

Griffin G
Posts: 89
Joined: Wed Sep 30, 2020 9:50 pm

### Re: Speed of light

For this class, I would use 2.99792 x 10^8 m.s^-1 because that is the value given on the constants and equations worksheet Lavelle sent in an email. However, whatever value you use just depends on how accurate you want to be.

alexandralopez 3F
Posts: 92
Joined: Wed Sep 30, 2020 10:11 pm

### Re: Speed of light

I would probably go off of the equations sheet Lavelle wants us to use! Its on ccle if you still need it!

Lizbeth Garcia 1F
Posts: 92
Joined: Wed Sep 30, 2020 9:39 pm

### Re: Speed of light

I agree with everyone else, use the one that lavelle will provide on the equation sheet.

Thomas Gimeno
Posts: 79
Joined: Wed Sep 30, 2020 9:49 pm

### Re: Speed of light

I wouldn't worry too much because usually the answer accounts for a slight bit of variation based on constants but i think if the text book is using 2.998*10^8 then it's probably your best bet.

Marco Vivar 3G
Posts: 90
Joined: Tue Feb 25, 2020 12:15 am

### Re: Speed of light

Use the equation sheet. The eq sheet has it listed as c=2.99792*10^8 m/s

Susanna Givan 2B
Posts: 61
Joined: Thu Feb 27, 2020 12:16 am

### Re: Speed of light

Is c a constant?

Alexa Pham 1D
Posts: 69
Joined: Wed Sep 30, 2020 10:03 pm

### Re: Speed of light

Susanna Givan 1L wrote:Is c a constant?

Yes, c is a constant for the speed of light (3.0 x 10^8 m/s)

Keeryth Sandhu 1H
Posts: 97
Joined: Wed Sep 30, 2020 10:04 pm

### Re: Speed of light

It's probably the safest just to use the constant on our formula sheet.

Nandhini Ekambaram 1L
Posts: 107
Joined: Wed Sep 30, 2020 9:58 pm

### Re: Speed of light

For most problems using 3.0 x 10^8 m/s resulted in the correct answer. But for exams, it would be safer to go with the more precise value given on the formula sheet.

Yolanda_Xing_3A
Posts: 43
Joined: Wed Sep 30, 2020 9:52 pm

### Re: Speed of light

I don’t think using either numbers would change the your answer since tests are in MC. Or else, staying with the equation sheet is no wrong.

Andy Hernandez
Posts: 56
Joined: Wed Sep 30, 2020 9:50 pm

### Re: Speed of light

2.998*10^8

Jacob Schwarz-Discussion 3I
Posts: 81
Joined: Wed Sep 30, 2020 10:01 pm

### Re: Speed of light

Lavelle is okay with 3*10^8! You don't need to worry about 2.999 he wants us to stick with 3 (:

Jacob Schwarz-Discussion 3I
Posts: 81
Joined: Wed Sep 30, 2020 10:01 pm

### Re: Speed of light

Lavelle is okay with 3*10^8! You don't need to worry about 2.999 he wants us to stick with 3 (: