Physics, 24.12.2019 05:31 charlesrogers38

Early black-and-white television sets used an electron beam to draw a picture on the screen. the electrons in the beam were accelerated by a voltage of 3.0 kv m kv; the beam was then steered to different points on the screen by coils of wire that produced a magnetic field of up to 0.67t

a

what is the speed of electrons in the beam?

b

what acceleration do they experience due to the magnetic field, assuming that it is perpendicular to their path? what is this acceleration in units of g image for early black-and-white television sets used an electron beam to draw a picture on the screen. the electrons in?

c

if the electrons were to complete a full circular orbit, what would be the radius?

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Answer from: derick263

A) $3.25\cdot 10^7 m/s$

Assuming the electrons start from rest, their final kinetic energy is equal to the electric potential energy lost while moving through the potential difference $\Delta V$ :

$K=\frac{1}{2}mv^2 = q\Delta V$

where

$m=9.11\cdot 10^{-31}kg$ is the mass of each electron

v is the final speed of the electrons

$q=1.6\cdot 10^{-19}C$ is the charge of the electrons

$\Delta V=3.0 kV=3000 V$ is the potential difference

Solving the equation for v, the speed, we find

$v=\sqrt{\frac{2q\Delta V}{m}}=\sqrt{\frac{2(1.6\cdot 10^{-19}C)(3000 V)}{9.11\cdot 10^{-31} kg}}=3.25\cdot 10^7 m/s$

B) Centripetal acceleration, $3.82\cdot 10^4 m/s^2$ , in units of g: 3898 g

When the electrons cross the region of the magnetic field, they experience a magnetic force which is perpendicular to their trajectory: therefore they start moving in a circular motion. The acceleration they experience is not tangential, but centripetal, and it is given by

$a_c = \frac{v^2}{r}$

where v is the speed and r the radius of the trajectory.

We can equate the magnetic force exerted on the electrons to the centripetal force:

qvB=ma_c

and isolate a_c to find the centripetal acceleration:

$a_c = \frac{qvB}{m}=\frac{(1.6\cdot 10^{-19} C)(3.25\cdot 10^7 m/s)(0.67 T)}{9.11\cdot 10^{-31} kg}=3.82\cdot 10^4 m/s^2$

And since g=9.81 m/s^2 , the acceleration can be rewritten as

$a_c = \frac{3.82\cdot 10^4 m/s^2}{9.81 m/s^2}=3898 g$

c) $2.76\cdot 10^{10} m$

The radius of the circular trajectory can be found by using the formula for the centripetal acceleration:

$a_c = \frac{v^2}{r}$

Solvign for r, we find

$r=\frac{v^2}{a_c}=\frac{(3.25\cdot 10^7 m/s)^2}{3.82\cdot 10^4 m/s^2}=2.76\cdot 10^{10} m$

Answer from: Quest

elly's long hair:

a. if the salon only takes cash, then this isn't the problem. it doesn't matter how much she has in her checking account. she can't get a haircut until she has the cash.

b. if she has overdraft protection, then there's no problem. she can go ahead and write a check that her account can't cover, then sometime later, pay the bank some outrageous usury for loaning her a few bucks for a few days, but with beautiful hair.

c. if elly has some principles, and doesn't want to write a bad check, then now she has a problem. her desire for the new hairstyle is in conflict with her honesty and integrity.

d. if the bank will not process a check she writes, then even if she had a million $$ in her account, she couldn't use any of it. the amount she has in her account is not the problem. and if i may suggest, she might as well close her checking account, and put the money where it'll work for her. it's not doing her a bit of good in a checking account, since she can't write any checks.

justin can't pay the full balance:

a. he can't even handle the credit limit he has now. under no circumstances should he ask for a higher limit.

b. he can ask for the grace period to be extended. but that's no solution, the bank will almost certainly refuse anyway, and there are much better options. he knew the rules of his credit card when he started using it.

c. he definitely should pay the interest on the balance, plus as much of the balance as he can cover at the same time.

d. he definitely should pay the minimum otherwise they could shut down his card. he should also pay as much more as he possibly can. he should also remember the awkward situation he's in, stop buying stuff on credit that he can't afford, and avoid adding any more debt.

i'd say that justin's best best option isn't on this list of choices. what he has to do: pay as much as he can at least the minimum payment plus as much more as he can and then avoid adding more debt.

Answer from: Quest

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