Potential Diffrence And Static Electricity

Question 1

Potential difference

Answer 1

The … (V) between two points in an electric field is the work done in bringing a charge of +1 C from one point to the other

• is a scalar quantity (work and energy are scalar)
• sometimes called voltage
• is the potential energy difference per coulomb
• can be measured with a voltametre or approximately with a electroscope

Question 2

Unit of potential difference

Answer 2

The unit of … is the joule per coulomb (J C^-1). This unit is also called the volt (V).

Question 3

The volt

Answer 3

The potential difference between two points is 1 volt if 1 joule of work is done when 1 coulomb is brought from one point to the other.

1 volt = 1 joule per coulomb
1 V = 1 J C^-1

Question 4

Electric current

Answer 4

An electric current is a flow of electric charge

Question 5

Potential at a point

Answer 5

The potential difference between a point and the earth is called the potential of that point

• the earth is at 0 potential
• note that as you add positive (+) charge to a conductor it becomes more difficult to bring a charge of +1C from earth to it, thus its potential increases

Question 6

Capacitance

Answer 6

The capacitance (C) of a conductor is the ratio of the charge on the conductor to its potential, i.e. C=Q/V

• the capacitance of a charged conductor is increased by bringing an oppositely charged conductor or an earthed conductor near it
• a capacitor can store charge

Question 7

Unit of capacitance

Answer 7

The unit of capacitance is the farad (F)

Question 8

The farad

Answer 8

A conductor has a capacitance of 1 farad if placing a charge if 1 C on it raises its potential by 1 volt, i.e.

1 farad = 1 coulomb per volt (C V^-1)

Question 9

Potential of a conductor

Answer 9

The charges on a conductor aren’t moving so all points on a conductor are at the same potential

Question 10

Dielectric

Answer 10

A parallel plate capacitor that consist of two parallel plates separated by an insulator.

Question 11

Common uses of capacitors

Answer 11

• allows alternating current (a.c) to flow through it but locks direct current (d.c)
• a variable capacitor is used to tune to a particular station on a radio
• capacitors are used to smooth out variations in direct current
• capacitors are used in a camera flash gun. The capacitor is charged slowly from a battery and discharged quickly through the bulb giving the flash
• capacitors can be used to allow alternating signals of certain frequencies past, but block others in a process called filtering