How Do You Calculate Magnetic Fields and Forces in Physics Problems?

[yhan89]

Homework Statement

1) What current would along straight wire have to carry in order that the magnetic field it produced was the same as the Earth's field, at a distance of 3.0 cm from the wire?

2) A heavy atom loses 3 of its electrons when bombarded by X-rays. It is then accelerated by a potential difference of 180 V, only to pass through a magnetic field of 0.028 T, where the ion is noted to be deflected into the arc of a circle of radius 0.32 m.

a) Find the mass of the ion, in kilograms, and atomic mass units.
b) state its probable type of ion. Note that you will need your periodic table for this part.
c) Why might you suspect that there is something 'fishy' with this data?


3) A proton that has been accelerated through a potential difference has a momentum of 3.4 x 10^-20 kg m/s as it enters a uniform magnetic field at right angles to the field. It is then defleted along the arc of a circle of radius 0.23 m.

a) Find its speed as it enter the field.
b) Find the strength of the magnetic field.
c) Find the kinetic energy of the proton as it enters the magnetic field.
d) What was the value of the potential difference that accelerated the proton, assuming it started from rest?
e) Fine the magnitude of the magnetic force acting on the proton while in the magnetic field.
f) Why doesn't the proton speed up or slow down whiel in the magnetic field?

Homework Equations

I don't even know how to start!
Sorry Help me.

The Attempt at a Solution

 

[berkeman]

Homework Statement

1) What current would along straight wire have to carry in order that the magnetic field it produced was the same as the Earth's field, at a distance of 3.0 cm from the wire?

2) A heavy atom loses 3 of its electrons when bombarded by X-rays. It is then accelerated by a potential difference of 180 V, only to pass through a magnetic field of 0.028 T, where the ion is noted to be deflected into the arc of a circle of radius 0.32 m.

a) Find the mass of the ion, in kilograms, and atomic mass units.
b) state its probable type of ion. Note that you will need your periodic table for this part.
c) Why might you suspect that there is something 'fishy' with this data?


3) A proton that has been accelerated through a potential difference has a momentum of 3.4 x 10^-20 kg m/s as it enters a uniform magnetic field at right angles to the field. It is then defleted along the arc of a circle of radius 0.23 m.

a) Find its speed as it enter the field.
b) Find the strength of the magnetic field.
c) Find the kinetic energy of the proton as it enters the magnetic field.
d) What was the value of the potential difference that accelerated the proton, assuming it started from rest?
e) Fine the magnitude of the magnetic force acting on the proton while in the magnetic field.
f) Why doesn't the proton speed up or slow down whiel in the magnetic field?

Homework Equations

I don't even know how to start!
Sorry Help me.

The Attempt at a Solution

Start at the beginning. For #1, what is the magnitude of the Earth's magnetic field at its surface? You can use wikipedia.org to find it if it's not in your book (be careful to work all in mks units). Then, what is the equation for the magnetic field B at some distance from a current carrying wire? Your book definitely has that. Then just do some math to answer #1.

Show us your work, then move on to #2.