electricity 1

what are the two types of charge?

negative and positive charges.

what do like charges do?

they repel

what do opposite charges do?

they attract

what are neutral objects?

neutral objects have the same number of positive and negative charges

are neutral objects able to repel/attract other neutral objects?

no.

atomic charge

when atoms gain or lose electrons they become charged. the charge is: charge = number of protons - number of electrons

when does an atom have a positive charge?

more protons than electrons

when does an atom have a negative charge?

more electrons than protons.

when does an atom have neutral charge?

equal number of protons and electrons

what is an ion?

an atom with a positive or negative charge.

si unit for charge

coulomb (C)

charges of subatomic particles

electron: -1.60×10^-19C
proton: 1.60×10¹⁹C

neutron: 0C

what is electrostatic induction?

charged objects attract uncharged (or neutral) objects due to an induced electric charge. induction is a temporary separation of some electrons from their atoms when an electrically charged object is placed near them. the induced charge disappears when the electrically charged object is removed. (positively charged atoms do not move)

what is an insulator?

refers to materials which do not conduct electricity as they have no free electrons or ions. they can maintain an induced charge.

examples of insulators

non-metals, plastics, paper, ceramics

what are conductors?

materials which conduct electricity because they have delocalised electrons. quickly dissipate their induced charge.

examples of conductors

metals

why is water attracted to charge?

water is dipolar. the oxygen atom is more electronegative than hydrogen, so electrons are pulled towards oxygen the atom. the oxygem atom is left with a small negative charge and the hydrogen atom with a small positive charge. the charged ends are attracted by the charged ends of other water molecules, dissolved ions and charged objects.

voltage source

forces negative charges (electrons) to the negative terminal. it also strips electrons from the positive terminal. negative terminal builds up excess negative charge (electrons) and the positive terminal builds up excess postive charge (lack of electrons). connecting the terminals allows the electrons to flow towards the positive terminal.

electrical work

in a voltage source work is done when moving the negative charge to the negative terminal (overcoming repulsive force). repulsive force is overcome and the charge is moved through a distance.

what is electric potential energy?

refers to what the work done on the charge is stored as

voltage

1 J of work moving 1 C of charge results in 1 V of electrical potential.

potential difference

as an electron flows through a circuit element, it loses potential energy. potential difference refers to the difference in potential energy per unit charge between two points on a circuit. also known as voltage (measured in V).

electric current

amount of charge which flows through a circuit every second

how do electrons flow through a circuit?

when there is an electrical potential difference in a circuit, the electrons are attracted to the positive terminal, causing electrons to flow through the circuit.

what is conventional current?

scientifiic convention which assumes that current flows in the opposite direction to the flow of electrons.

alternating current

current flows in both directions because the voltage which pushes the current alternates direction.

direct current

current only flows in one direction.

how fast in an electron?

electrons are pulled slowly along an electrical circuit (0.33mm/s), small KE.

resistance

the measure of opposition to the flow of electric current. unit is ohm.

resistance and current relationship

a circuit resistance acts to resist the flow of current; the larger the resistance the harder it is to push electrons through the circuit.

what happens when the flow of electrons is resisted?

energy converts to other forms such as heat and light etc.

factors that affect resistance

material type, length of the conductor, cross-sectional area, temperature, resistivity

ohm’s law

V = IR

ohmic conductor

constant resistance → linear V vs I graph

non-ohmic conductor

resistance depends on current → non-linear V vs I graph

electrical power

refers to the rate that energy is transformed in a circuit

electrical energy

W = P x t = VI x t = I²R x t