# Charged particles moving through a magnetic field

## Homework Statement

A collection of charged particles move through a magnetic field at an angle to the field lines.
Calculate the velocity of the particle if it is an electron moving at 30 degrees to the magnetic field of strength 3.4mT, causing it to experience a force of 4.7x106-18N

F=BqVSin(Theta)

## The Attempt at a Solution

4.7x10^-18 / ((3.410^-3)(1.602x10^-19)(Sin(30))) = 8733.44m/s

## Answers and Replies

gneill
Mentor
Your method looks fine, but your result is incorrect. Check that your calculator is set to use degrees rather than radians for angles. Or, just recall what the value of sin(30°) is and use it: it's a very common angle and it's sine and cosine really should be memorized.

KieranRC
Your method looks fine, but your result is incorrect. Check that your calculator is set to use degrees rather than radians for angles. Or, just recall what the value of sin(30°) is and use it: it's a very common angle and it's sine and cosine really should be memorized.
Okay great thank you

rude man
Homework Helper
Gold Member

## Homework Statement

A collection of charged particles move through a magnetic field at an angle to the field lines.
Calculate the velocity of the particle if it is an electron moving at 30 degrees to the magnetic field of strength 3.4mT, causing it to experience a force of 4.7x106-18N

F=BqVSin(Theta)

## The Attempt at a Solution

4.7x10^-18 / ((3.410^-3)(1.602x10^-19)(Sin(30))) = 8733.44m/s
Your answer is off by a factor of about 2. If you ignored the sin in the denominator you'd be close but still off by about 1%.

KieranRC
Your answer is off by a factor of about 2. If you ignored the sin in the denominator you'd be close but still off by about 1%.
but if i take the sin out the dont i take out the angle altogether? and then doesnt that equation without sin just assum the angle is 90?
How do i go about correcting my answer so it is spot on?
Thanks

gneill
Mentor
|sin(30 rad)/sin(30 deg)| ~= 2. Did you check your calculator deg/rad setting as I suggested?

Type in sin(30) right now. What do you get?

|sin(30 rad)/sin(30 deg)| ~= 2. Did you check your calculator deg/rad setting as I suggested?

Type in sin(30) right now. What do you get?
Yes i did, and in the end i git 17257.84m/s (by changing to deg)

rude man
Homework Helper
Gold Member
but if i take the sin out the dont i take out the angle altogether? and then doesnt that equation without sin just assum the angle is 90?
How do i go about correcting my answer so it is spot on?
Thanks
No, you need to leave the sin term in. I just observed that without it you'd be close, but that was just a coincidence and to give you a hint as to what the answer might be.

Your problem, simply, is your math! And BTW you stated in your original post that " ..experience a force of 4.7x106-18N .. ". What does that mean?
BTW setting your calculator to radians instead of degrees is not the problem either.

No, you need to leave the sin term in. I just observed that without it you'd be close, but that was just a coincidence and to give you a hint as to what the answer might be.

Your problem, simply, is your math! And BTW you stated in your original post that " ..experience a force of 4.7x106-18N .. ". What does that mean?
BTW setting your calculator to radians instead of degrees is not the problem either.
The forced experienced is just what the question stated.

re-entering everything in and i get 17279.4m/s does this seem more accurate?

gneill
Mentor
The forced experienced is just what the question stated.

re-entering everything in and i get 17279.4m/s does this seem more accurate?
That result looks good to me. Be sure to round to the appropriate number of significant figures before submitting your result.

rude man
Homework Helper
Gold Member
The forced experienced is just what the question stated.

re-entering everything in and i get 17279.4m/s does this seem more accurate?
Yes, surely does!

rude man
Homework Helper
Gold Member
@gneill, seems your suggestion to check for rads rater than sines was correct after all.