4.1.1 - Charge

Question 1

What is electric current?

Answer 1

Electric current is the rate of flow of charge

Question 2

What is 1 Coulomb?

Answer 2

One coulomb is defined as the amount of charge that passes in one second when the current is one ampere

Question 3

What is the equation linking charge, time and current?

Answer 3

I = Q/t
Current = Charge/time

Question 4

What is electric current measured in?

Answer 4

Current is measured in Coulombs (C)

Question 5

What is the charge of the electron and proton?

Answer 5

electron: -e
proton: +e

where e is the elementary charge

Question 6

What is electric charge?

Answer 6

Electric charge is a physical property that all bodies posses, like temperature,volume etc. Charge can be positive or negative

Question 7

What force do charges interact via and what are their interactions?

Answer 7

Electric charges interact via the electrostatic force:

• Two like charges repel
• Two unlike charges attract

Question 8

Electrons are the ___ of a circuit

Answer 8

charge carriers

Question 9

what is the elementary charge?

Answer 9

e =1.6 * 10^-19

Question 10

What is the equation linking number of electrons, charge and elementary charge?

Answer 10

Q = ne
charge = no. of electrons * elementary charge

Question 11

What does net charge on an object being quantised mean?

Answer 11

Quantised means that charge on an object can only have certain values. These are integer multiples of e, since e is the smallest unit of charge

Question 12

What is the main reason for net charge on most objects?

Answer 12

net charge on most objects ends up from gain or loss of electrons. Added electrons leave a negative net charge and removed a positive net charge

Question 13

What is the difference between electric currents in metals vs electrolytes?

Answer 13

In metals an electric current is usually caused by a flow of electrons, whereas in electrolytes the charge carriers are ions.

Question 14

Why can metals conduct electricity?

Answer 14

Most electrons in metal atoms remain fixed to their atom,but a small number (coming from the outermost shell) are free to move. These delocalised electrons are the charge carriers.

Question 15

What two things can a greater current in a metal be caused by?

Answer 15

1) A greater number of electrons moving past a given point each second
2) Same number of electrons moving faster through the metal

Question 16

What are electrolytes?

Answer 16

electrolytes are liquids that carry electric current

Question 17

what two types of electrolyte are there?

Answer 17

all electrolytes are either molten ionic compounds or ionic solutions

Question 18

Why does salt dissolved in water cause a current to flow when an anode and cathode are placed in the solution?

Answer 18

1) The salt separates into positively charged sodium ions and negatively charged chloride ions when dissolved in water
2) The Na+ Ions are attracted towards the cathode (negative electrode) and Cl- to the anode (positive)
3) This movement of ions is a flow of charge, a current
4) At the cathode Na+ ions accept an electron and at the anode Cl- ions donate one so electrons can flow through the metal part of the circuit

Question 19

What is the difference between conventional current and electron flow?

Answer 19

While conventional current is always treated as flowing from positive to negative (regardless of movement of charge carriers), electron flow moves from negative to positive

Question 20

What is the law of conservation of charge?

Answer 20

Electric charge can neither be created or destroyed - so in an interaction total charge before and after must be the same

Question 21

What is Kirchoff’s first law?

Answer 21

It states that for any point in an electrical circuit, the sum of currents into the point = the sum of currents out of it

Question 22

What is Kirchoff’s first law due to?

Answer 22

The law is due to conservation of charge, since current is a charge over time, charge carriers entering a point must be the same as those leaving it over that period of time