Static electricity

Question 1

Atomic nature of static charge

Answer 1

objects place in contact with each other electrons can be knocked off from one of the material
Only electrons can move

Question 2

Insulators

Answer 2

substance that electric charge does not flow through
static charge can only build up on insulators

Question 3

Conductors

Answer 3

substance that electric charge can flow through

Question 4

Gold leaf electroscope uses 1

Answer 4

Detect charge: when a charged object is brought near the electroscope induced charges appear on it and leaf diverges

Question 5

Gold leaf electroscope uses 2

Answer 5

Indicate the approximate size of the charge: The larger the charge on the object, the larger the charge on the leaf

Question 6

Gold leaf electroscope uses 3

Answer 6

Test whether the charge is positive or negative: If leaf diverges its the same charge, is it collapses it is opposite charge

Question 7

Gold leaf electroscope uses 4

Answer 7

Test if an object is a conductor or insulator: If leaf collapse then its a conductor

Question 8

Distribution of charge on a insulated conductor

Answer 8

static charge on a conductor tends to accumulate on the outside where the conductor is most pointed

Question 9

Point discharge

Answer 9

Large charge is gathered on a point in a conductor
Ions that are free to move in the air are either attracted or repelled away
Moving ions produces more ions by colliding with atoms in the air
Ions that are repelled form “electric wind”

Question 10

E.g. of static electricity

Answer 10

Lightening is a result of large amount of static electricity being discharged from clouds
Crackling and clinging of synthetic clothes. Crackling due to small sparks
Aeroplanes can build up large amount of static charge in flight due to friction, must be discharged before the plane is refuelled

Question 11

Lightening conductors

Answer 11

Prevents the building from getting hit by lightening
When clouds with large charge passes over the conductor, charges are induced on the rod
This induced charges cause point discharge to take place, lowering the charge between the cloud and the rod reducing the chance of a lightening charge

Question 12

Coulomb’s Law

Answer 12

Force of attraction or repulsion between any two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between them
Direction of the force is always along the line joining the two charges
The size of the force depends on the medium that surrounds it. The greatest force is when it is in a vacuum

Question 13

Permitivity

Answer 13

If the material between the charges is air, it is close to the permittivity of a vacuum or of free space (constant value)
relative permittivity of medium x permittivity of vacuum = permittivity of medium

Question 14

Electric fields

Answer 14

Any region where a static charge experiences a force other than the force of gravity
Always caused by other static charges in the vicinity

Question 15

Electric Field lines

Answer 15

line drawn in an electric field showing the direction of a force on a positive charge placed in the field
The stronger the field the closer together the field lines

Question 16

To show electric field lines

Answer 16

Oil
Semolina - Powder showing electric field lines

Question 17

Application of electric fields

Answer 17

Electric charge is transferred onto the particles through point discharge
Plates carrying opposite charge to which the particles are attracted to

Question 18

Electrostatic precipitators

Answer 18

Device that removes smoke and dues particles from dirty air

Question 19

Xerography (photocopying)

Answer 19

The drum in a photocopier is charged electrostatically. The image of the document to be copied is focused onto it.
Light causes the charge to escape from the drum
Toner particles are attracted to the remaining charged areas giving a copy of the document on the drum
Image is transferred onto a sheet of paper and fixed in place with ink

Question 20

Effect of an electric field on integrated circuit

Answer 20

When atmospheric conditions are right the body can build up large amount of static charge - discharge in the form of spark
If the spark passes through an integrated circuit which are very sensitive to current, it is likely to damage it
To prevent this person working with integrated circuit are connected to earth before working on them

Question 21

Electric field strength

Answer 21

Electric field strength at a point in an electric field is the force per unit charge at that point
E=F/Q
Unit Newton per coulomb