# Constituents of the Atom QP help

Watch
Announcements

Page 1 of 1

Go to first unread

Skip to page:

Could anyone help me with this question? I have no idea how to start no matter how much I look at it. It's Q2 of this link: https://pmt.physicsandmathstutor.com...0Atom%20QP.pdf

0

reply

Report

#2

First the direction, up or down.

If the ion is positive then the electric field direction needs to oppose and balance the downwards force on the ion due to gravity.This gives the direction of the field.

The magnitude of the field needs to balance the weight of the ion.

Its weight is mg downwards.

You know that if the field is of strength E then the force on a charge q is = Eq

Finally they give you a value for q/m for the ion as 2.4 x 10

This info, rearranged a bit and equated, will give you a value for E.

If the ion is positive then the electric field direction needs to oppose and balance the downwards force on the ion due to gravity.This gives the direction of the field.

The magnitude of the field needs to balance the weight of the ion.

Its weight is mg downwards.

You know that if the field is of strength E then the force on a charge q is = Eq

Finally they give you a value for q/m for the ion as 2.4 x 10

^{7}This info, rearranged a bit and equated, will give you a value for E.

1

reply

(Original post by

First the direction, up or down.

If the ion is positive then the electric field direction needs to oppose and balance the downwards force on the ion due to gravity.This gives the direction of the field.

The magnitude of the field needs to balance the weight of the ion.

Its weight is mg downwards.

You know that if the field is of strength E then the force on a charge q is = Eq

Finally they give you a value for q/m for the ion as 2.4 x 10

This info, rearranged a bit and equated, will give you a value for E.

**Stonebridge**)First the direction, up or down.

If the ion is positive then the electric field direction needs to oppose and balance the downwards force on the ion due to gravity.This gives the direction of the field.

The magnitude of the field needs to balance the weight of the ion.

Its weight is mg downwards.

You know that if the field is of strength E then the force on a charge q is = Eq

Finally they give you a value for q/m for the ion as 2.4 x 10

^{7}This info, rearranged a bit and equated, will give you a value for E.

0

reply

Report

#4

The direction of an electric field is, by definition, the direction of the force on a

So to balance the gravitational force downwards on the positive ion, the electric force needs to be upwards.

So the electric field needs to be directed upwards.

This is in order to hold the ion stationary. The two forces are balanced. Gravity downwards and the electric field upwards.

In the calculation, you are equating these 2 forces, mg downwards and the electric field force upwards

so Eq = mg where q is the charge on the ion and m is its mass

so

E=mg/q

We are given the charge to mass ratio of this ion which means we have a value of q/m

This eliminates q and m.

We also have a value for g, so we can find E.

When doing a question like this, asking you to find E, the first thing I would do is write down any equation I know with E in it and which involves charge and force. These are the things in the question.

So I think of F=Eq for the ion.

As it is being suspended I think of the ion's weight, mg, being balanced and equal to that force Eq.

Just find and try more similar questions. After a while, the pattern and method will be familiar.

**positive**charge.So to balance the gravitational force downwards on the positive ion, the electric force needs to be upwards.

So the electric field needs to be directed upwards.

This is in order to hold the ion stationary. The two forces are balanced. Gravity downwards and the electric field upwards.

In the calculation, you are equating these 2 forces, mg downwards and the electric field force upwards

so Eq = mg where q is the charge on the ion and m is its mass

so

E=mg/q

We are given the charge to mass ratio of this ion which means we have a value of q/m

This eliminates q and m.

We also have a value for g, so we can find E.

When doing a question like this, asking you to find E, the first thing I would do is write down any equation I know with E in it and which involves charge and force. These are the things in the question.

So I think of F=Eq for the ion.

As it is being suspended I think of the ion's weight, mg, being balanced and equal to that force Eq.

Just find and try more similar questions. After a while, the pattern and method will be familiar.

0

reply

(Original post by

The direction of an electric field is, by definition, the direction of the force on a

So to balance the gravitational force downwards on the positive ion, the electric force needs to be upwards.

So the electric field needs to be directed upwards.

This is in order to hold the ion stationary. The two forces are balanced. Gravity downwards and the electric field upwards.

In the calculation, you are equating these 2 forces, mg downwards and the electric field force upwards

so Eq = mg where q is the charge on the ion and m is its mass

so

E=mg/q

We are given the charge to mass ratio of this ion which means we have a value of q/m

This eliminates q and m.

We also have a value for g, so we can find E.

When doing a question like this, asking you to find E, the first thing I would do is write down any equation I know with E in it and which involves charge and force. These are the things in the question.

So I think of F=Eq for the ion.

As it is being suspended I think of the ion's weight, mg, being balanced and equal to that force Eq.

Just find and try more similar questions. After a while, the pattern and method will be familiar.

**Stonebridge**)The direction of an electric field is, by definition, the direction of the force on a

**positive**charge.So to balance the gravitational force downwards on the positive ion, the electric force needs to be upwards.

So the electric field needs to be directed upwards.

This is in order to hold the ion stationary. The two forces are balanced. Gravity downwards and the electric field upwards.

In the calculation, you are equating these 2 forces, mg downwards and the electric field force upwards

so Eq = mg where q is the charge on the ion and m is its mass

so

E=mg/q

We are given the charge to mass ratio of this ion which means we have a value of q/m

This eliminates q and m.

We also have a value for g, so we can find E.

When doing a question like this, asking you to find E, the first thing I would do is write down any equation I know with E in it and which involves charge and force. These are the things in the question.

So I think of F=Eq for the ion.

As it is being suspended I think of the ion's weight, mg, being balanced and equal to that force Eq.

Just find and try more similar questions. After a while, the pattern and method will be familiar.

0

reply

Report

#6

You don't need to find g. It is always given as a value either in the question itself, or in the data list for the examination.

It's usually either 9.8 or 9.81 m/s

Whatever value is given.

So when you get

Eq = mg and rearrange to get

E=mg/q

I imagine you are given the value of g to be 9.81 m/s2 as the answers for A to D are given to 3 significant figures.

You are given the charge to mass ratio q/m for the ion as 2.40 x 10

so in the formula you have there m/q is 1 / 2.40 x 10

This question touches on 2 topic areas in physics.

1) Electric fields

2) Atomic physics - in particular, a) Millikan's experiment to measure charge by suspending a charged particle in an electric field, and b) measurement of the mass of an ion using a mass spectrometer.

Take a look in those topic areas to find possible similar questions.

It's usually either 9.8 or 9.81 m/s

^{2}Sometimes even 10m/s^{2}Whatever value is given.

So when you get

Eq = mg and rearrange to get

E=mg/q

I imagine you are given the value of g to be 9.81 m/s2 as the answers for A to D are given to 3 significant figures.

You are given the charge to mass ratio q/m for the ion as 2.40 x 10

^{7}so in the formula you have there m/q is 1 / 2.40 x 10

^{7}This question touches on 2 topic areas in physics.

1) Electric fields

2) Atomic physics - in particular, a) Millikan's experiment to measure charge by suspending a charged particle in an electric field, and b) measurement of the mass of an ion using a mass spectrometer.

Take a look in those topic areas to find possible similar questions.

1

reply

(Original post by

You don't need to find g. It is always given as a value either in the question itself, or in the data list for the examination.

It's usually either 9.8 or 9.81 m/s

Whatever value is given.

So when you get

Eq = mg and rearrange to get

E=mg/q

I imagine you are given the value of g to be 9.81 m/s2 as the answers for A to D are given to 3 significant figures.

You are given the charge to mass ratio q/m for the ion as 2.40 x 10

so in the formula you have there m/q is 1 / 2.40 x 10

This question touches on 2 topic areas in physics.

1) Electric fields

2) Atomic physics - in particular, a) Millikan's experiment to measure charge by suspending a charged particle in an electric field, and b) measurement of the mass of an ion using a mass spectrometer.

Take a look in those topic areas to find possible similar questions.

**Stonebridge**)You don't need to find g. It is always given as a value either in the question itself, or in the data list for the examination.

It's usually either 9.8 or 9.81 m/s

^{2}Sometimes even 10m/s^{2}Whatever value is given.

So when you get

Eq = mg and rearrange to get

E=mg/q

I imagine you are given the value of g to be 9.81 m/s2 as the answers for A to D are given to 3 significant figures.

You are given the charge to mass ratio q/m for the ion as 2.40 x 10

^{7}so in the formula you have there m/q is 1 / 2.40 x 10

^{7}This question touches on 2 topic areas in physics.

1) Electric fields

2) Atomic physics - in particular, a) Millikan's experiment to measure charge by suspending a charged particle in an electric field, and b) measurement of the mass of an ion using a mass spectrometer.

Take a look in those topic areas to find possible similar questions.

1

reply

X

Page 1 of 1

Go to first unread

Skip to page:

### Quick Reply

Back

to top

to top