P5.2 - Electrical quantities Flashcards
Objects become charged when
they gain or lose electrons
Charge is measured in
Coulombs (C)
An objective can be either
negatively or positively charged
Two positive or two negative charges will
repel
Two opposite charges will
attract
When there is a difference between positive and negative charge of two objects it is called
potential difference
potential difference causes
a rapid transfer of charge known as static electricity in which a spark is produced
Suggest why clothes dried in a tumble drier might stick to each other.
The clothes will rub against each other which would charge the clothes as electrons are lost when the clothes rub together. Some will lose electrons and become positively charged and others will gain electrons and become negatively charged. The clothes that are oppositely charged will attract each other and stick together.
Rubbing an object against another object will cause
electrons to jump from one object to another causing charges to form between both objects
Substances that allow electric charge to pass through are called
electrical conductors (all metals are electrical conductors)
Substances that do not allow electric charge to pass through are called
electrical insulators (glasses and plastics)
When you charge an object with static electricity you are
adding or taking away negatively charged electrons so the charge on the object becomes unbalanced
Example of change in charges
when you rub glass or a rode with cloth the electrons from the rod are rubbed onto the cloth so the cloth becomes negatively charged and the rod becomes positively charged
What is electrostatic forces
an attraction or repulsion due to electric charges.
Charged objects create
invisible electric fields around them
If another electrically charged object enters an electric field the charge will feel a
force acting on it
The strength of the force of an electric field depends on
how close the particles are: the closer the larger the force
how much electrical charge they carry: the more charge the larger the force
If a positive point charge exerts an electric field the direction will
be going away from the positive charge
If a negative point charge exerts an electric field the direction will
be going towards the negative charge
Electrical current is the
flow of electric charges
Electrical current is measured in
amps (A)
Conventional current flows from the
positive end of the battery to the negative end.
electrons flow from the
negative end of a battery to the positive end of the battery because they are negatively charged
current =
charge/time (I = Q/t)
Electrical insulators have no free
electrons so no charge can carry a current
electrical conductors have lots of
charges that a free to move, which in metals are electrons.
Potential difference (p.d) is measured in and by
volts (V) and voltmeter
electromotive force (e.m.f) measures
the amount of energy a energy source supplies to each charge passing through. (for example: a mobile phone battery provides an e.m.f of 3.8V to drive current through the phones circuit)
(e.m.f) is measured in
volts
potential difference (p.d) is the difference in
the amount of energy that charge carriers have between two points in a circuit
voltage =
amount of energy transferred / charge (V = E/Q)
Ammeters measure
the flow of current that passes through
Voltmeters measure
p.d between two points in circuit
Resistance is the measure of
how difficult it is for currents to flow through a compotent
charge flow is affected by
- The resistance: if resistance increase current decrease
2. The p.d: if p.d increase current increase
Resistance measured in
ohms (Ω)
what is ohms law
resistance between two points in circuit is equal to p.d between two points divided by current flowing through them. R = V/I
The resistance of a component can be found using a
circuit by placing the component (lamp or resistor) in a circuit with an ammeter to measure current and voltmeter to measure p.d.
a voltage current graph for a component where the resistance remains same shows a
direct proportion between p.d and current. This is ohmic resistor
For a particular conductor the resistance is
proportional to the length. The longer the conductor the further the electrons have to travel and the more likely they collide with metal ions meaning more resistance. A wire twice as long will have twice as much resistance
Resistance can be shown in a model of a conductor
as the electrons which represent the flow have to get passed the metal ions in which they collide causing resistance
Resistance is inversely proportional to the
cross sectional area of a wire. The greater the cross sectional area of a conductor the more electrons there are to carry charge along donators length so decrease resistance. Twice the cross sectional area half the resistance.
