Static Electricity

Question 1

Atomic nature of electric charges

Answer 1

• if an object is negatively charged (-) it has gained electrons
• if an object is positively charged (+) it has lost electrons
• it is only the electrons that actually move when objects become charged

Question 2

Unit of electric charge

Answer 2

The unit of electric charge is the coulomb (C).

1 coulomb is the amount of charge on about 6.25 x 10^18 electrons.

Question 3

Insulator

Answer 3

Any substance through which electric charge cannot flow is called an insulator
E.g glass, Perspex, most plastics

Question 4

Conductor

Answer 4

Any substance through which electric charge can flow is called a conductor
E.g. metals

A conductor from which charge cannot escape because it is insulated is called an insulated conductor

Question 5

Distribution of charge on an insulated conductor

Answer 5

• All static charge resides on the outside of a conductor

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

Question 6

The van de graafe generator

Answer 6

Is a machine that produces large amounts of static electricity on its dome and is suitable for electrostatic experiments in a school laboratory

Question 7

Coulomb’s law

Answer 7

States that the force of attraction or repulsion between two point charges is directly proportional, the product of the charges and inversely proportional to the square of the distance between them.

Is an example of an inverse square law - the force is inversely proportional to the square of the distance between the charges

The size of the force depends on the medium surrounding the charges. The force is greatest when the charges are in a vacuum.

Question 8

If the charges are Q1 and Q2 and the distance between them is d, the law states that:

Answer 8

F= 1 Q1Q2
– ——-
4pie d^2

Question 9

Electric field

Answer 9

An electric field is any region of space where a static electric charge experiences a force other than the force of gravity

An electric field is always caused by other static charges in the vicinity

Question 10

Line of force (electric field line)

Answer 10

An electric field line is a line drawn in an electric field showing the direction of the force on a positive charge placed in the field

Question 11

Electric field strength

Answer 11

The electric field strength E at a point in an electric field is the force per unit charge at that one point, i.e. electric field strength is the force per coulomb

Question 12

Unit of electric field strength

Answer 12

The unit of electric field strength is the Newton per coulomb (N c^-1).

Question 13

Applications of electric fields

Answer 13

• electrostatic precipitators
• xerography-the photocopier
• the effect of an electric field on integrated circuits

Question 14

A gold leaf electroscope can be used to detect the following:

Answer 14

• detect charge
• indicate the approximate size of charge
• test whether a charge is + or -
• test if an object is an insulator or a conductor
• indicate the size of a potential difference

Question 15

The size of the force between two static electric charges that each charge exerts on the other depends on?

Answer 15

• the size of each charge
• the distance between the charges
• the material surrounding the charges