Topic 4-Motion of particles

Question 1

What does it mean if an object is traveling in a circle and what force does this result in

Answer 1

It is constantly changing direction
Is therefore accelerating
There must be a resultant force which acts towards the centre of the circle called the centripetal force

Question 2

The force on a moving charge in a magnetic field is

Answer 2

Perpendicular to its direction of travel, causing the particle to follow a curved track

Question 3

What does the direction particles travel in a magnetic friend depend on

Answer 3

Positive or negative charge (opposite directions)

Question 4

Why do you see particles moving in spirals

Answer 4

Because particles lose energy as they interact with other particles
Less energy=more curved

Question 5

Why are magnetic fields used in particle accelerators such as cyclotrons

Answer 5

To make the particles move on a circular or spiral path

Question 6

What is a cyclotron

Answer 6

A particle accelerator which uses a magnetic field to accelerate particles at very high energies along circular paths

Question 7

How does a cyclotron work

Answer 7

1) charged particle starts in centre
2) two semicircular electrodes used to accelerate across gap
3) alternating potential difference applied between electrodes-particle attracted from one side to the other causing energy to decrease
4) the magnetic field maintains circular motion
5) causing particles to spiral out as energy increases

Question 8

What does proton enrichment form

Answer 8

Isotopes that emit positrons

Question 9

How does positron enrichment work

Answer 9

A proton is absorbed by nucleus causing the proton number to increase forming a new element
This needs a lot of energy (cyclotron used)
Radioisotopes formed by proton enrichment are positron emitters
Good in hospitals (PET scans)

Question 10

Give three examples of radioisotopes formed by proton enrichment

Answer 10

Fluorine-18
Carbon-11
Nitrogen-13

Question 11

How do particle accelerators help scientists find out more about the universe and some problems with this

Answer 11

Use them to smash particles together at tremendous speeds to see what happens to give clues
Done internally, is expensive and need specialist expertise
Rival groups looking at the same thing

Question 12

Example of collaborative work using proton enrichment

Answer 12

Large Hadron Collider at Geneva

CERN built the largest and most powerful accelerator to recreat collisions after the Big Bang

Question 13

Momentum is always

Answer 13

Conserved

Question 14

In elastic collisions

Answer 14

Momentum and kinetic energy is conserved

Question 15

In Inelastic collisions

Answer 15

Some kinetic energy is converted into other forms

Momentum is always conserved

Question 16

An example of Inelastic collisions and how kinetic energy is converted

Answer 16

Bouncing ball
Won’t bounce as high as you dropped it as gravitational potential energy is transferred into kinetic energy and lost when hits the ground (sound/heat)

Question 17

MOMENTUM=

Answer 17

MASS*VELOCITY

Question 18

What is the mass of both particles converted into and given of as in annihilation

Answer 18

Into energy which is given of as two gamma rays

Question 19

What happens in positron and electron annihilation

Answer 19

The position and electron collide head on at the same speed, opposite directions
They have the same mass and opposite velocities so momentum is 0
Momentum is conserved so the two gamma rays have a momentum of 0
So the gamma rays produced have the same energy but opposite velocities

Question 20

Why is the charge before and after annihilation 0

Answer 20

Electrons have a negative charge and positrons have a positive charge (-1,+1)
Gamma rays have no charge

Question 21

How is annihilation used in PET scanning

Answer 21

Positron emitting radioactive isotope is injected which collided with electrons in organs (annihilate—>gamma rays)
There is a higher take up in tumour cells than normal ones
Detectors around body detect pair of gamma rays which tumour lays along the path of
Detect three pairs to accurately locate tumour by triangulation

Question 22

What is velocity

Answer 22

Speed and direction of an object