MYTUTOR SUBJECT ANSWERS

430 views

Two electrons are a distance r apart, the first electron exerts a force F on the second electron. a) What force does the second electron exert on the first? b) In terms of r, at what distance is the force that the first electron exerts on the second F/9?

This question is on electric forces between charged particles. A useful equation to consider is Coulomb's law:

F=k(Q1Q2)/R2

Where k is the Coulomb's law constant:

k~9.0x109Nm2/C2

Q is the charge on each particle in Coulombs, R is the distance in metres and F is the force in Newtons.

a) This part is a simple application of Newton's third law, as the first electron is exerting a repulsive force F on the second, the second must also be exerting a repulsive force F on the first. (Every force has an equal and opposite reaction force!)

b) This section requires you to look at Coulomb's law. It is what is known as an inverse square law, this effectively means the force decreases proportionally to the square of the distance, so for the force to have decreased by a factor of 9, the distance must have increased by a factor of the square root of nine, this equals 3, so the new distance is 3r. Nothing else in the equation changes, so they all other terms can be treated as constants and ignored.

This can be seen more explicitly by mathematically manipulating Coulomb's law, however I find it easier and more useful to instead find the answer by just thinking about the underlying link between force and distance in this equation, this means you develop a proper understanding of the inverse square relationship.

Ross W. GCSE Physics tutor, A Level Physics tutor, GCSE Maths tutor, ...

10 months ago

Answered by Ross, an A Level Physics tutor with MyTutor


Still stuck? Get one-to-one help from a personally interviewed subject specialist

75 SUBJECT SPECIALISTS

Ashika V. GCSE Maths tutor, A Level Maths tutor, IB Maths tutor, 13 P...
£26 /hr

Ashika V.

Degree: Physics (Masters) - Manchester University

Subjects offered:Physics, Maths+ 2 more

Physics
Maths
Extended Project Qualification
-Personal Statements-

“Hi I'm Ashika, a third year MPhys Physics student at the University of Manchester. I tutor in Maths and Physics, Personal Statements and the EPQ.”

£22 /hr

Benedict C.

Degree: Natural Sciences (Bachelors) - Leeds University

Subjects offered:Physics, Maths

Physics
Maths

“I am studying Physical Natural Sciences at Leeds University. My sessions focus on understanding and making examples work for you.”

£24 /hr

Joe C.

Degree: General Engineering (Masters) - Durham University

Subjects offered:Physics, Science+ 2 more

Physics
Science
Maths
Computing

“Masters student at Durham University, ready to help you excel at Maths and Science ”

About the author

Ross W.

Currently unavailable: for new students

Degree: MPhys (Masters) - Durham University

Subjects offered:Physics, Maths+ 4 more

Physics
Maths
Further Mathematics
Chemistry
Biology
-Personal Statements-

“I am a second year student studying Physics at Durham University (very pleased with my first year results - got a 1st - yay!) I have always been fascinated by science and maths and their ability to explain the world around us. What Do...”

You may also like...

Posts by Ross

A rollercoaster carriage of mass 100kg has 45kJ of Kinetic Energy at the lowest point of its ride. Ignoring air resistance and friction between the wheels and the tracks, what is the maximum height above this point it could reach? [Take g as 10m/s/s)

Two electrons are a distance r apart, the first electron exerts a force F on the second electron. a) What force does the second electron exert on the first? b) In terms of r, at what distance is the force that the first electron exerts on the second F/9?

Other A Level Physics questions

Why does water stay in the bucket if it is swung through a loop fast enough?

When does a pendulum bob move fastest and why?

A ball is hit horizontally at a height of 1.2 m and travels a horizontal distance of 5.0 m before reaching the ground. The ball is at rest when hit. Calculate the initial horizontal velocity given to the ball when it was hit.

A ball is thrown out of a window 18m off the ground. It is thrown horizontally at 0.5m/s. Show that it takes about 2s to reach the ground

View A Level Physics tutors

We use cookies to improve your site experience. By continuing to use this website, we'll assume that you're OK with this. Dismiss

mtw:mercury1:status:ok