P4.2 - Electrical Quantities Flashcards
What’s the relationship between positive and positive charges? [1]
they repel
What’s the relationship between positive and negative charges? [1]
they attract
What’s the relationship between negative and negative charges? [1]
they repel
What happens to the force the closer the charges are? [1]
the greater the force between them
Where do charges come from? [1]
- when two materials are rubbed together
- electrons may be transferred from one to another
What are the charges of the materials being rubbed together? [2]
- one has a net negative charge
- one has a net positive charge
What are conductors? [1]
- materials that let electrons pass through them
What are the best electrical conductors? [1]
- metals
What makes ___ good thermal conductors and why? [2]
- metals
- because they have free electrons
What are insulators? [1]
- materials that hardly conduct at all
Why don’t insulators conduct? [2]
- electrons are held tightly to their atoms
- not free to move
How can electrons be transferred? [1]
by rubbing - static charging
What are examples of insulators? [3]
- plastics
- glass
- PVC
What are semi-conductors? [1]
neither an insulator or a conductor
What are the properties of semi-conductors? [2]
- poor conductors when cold
- better conductors when warm
What is charge measured in? [1]
Coulombs
What is Static Electricity? [2]
- charges which are not free to move
- charges are at rest
What does the charging of solids by friction involve? [1]
ONLY the transfer of negative charge (electrons)
What is an electric field? [2]
the region in which an electric charge experiences a force
How much is 1 micro coulomb in coulombs? [1]
10⁻⁶ C = one millionth of a coulomb
What are the two types of electricity? [2]
- Static
- Current
What is current? [2]
- when charges are moving
- when you can get the electrons to drift
What is an Electric Current? [1]
The rate of flow of charge
What is formula relating current and charge? [2]
Current = Charge / Time
What is the symbol formula for current? [1]
I = Q / T
What is the unit for current? [1]
Amperes
What is A.C.? [2]
- when the current swings back and forth in every halfcycle
What is D.C? [1]
- current only flows in one direction
What is electrical conduction in metals? [1]
- the movement of delocalised electrons
Where is conventional current from? [1]
POSITIVE TO NEGATIVE
Where is the flow of electrons from? [1]
NEGATIVE TO POSITIVE
What is the use of an ammeter? [2]
- measures current
- how much charge flows per second through the wire
What is the use of a voltmeter? [1]
tool used to measure voltage
What is Electromotive Force (E.M.F)? [3]
the electrical work done by a source in moving a unit charge around a complete circuit
What is E.M.F measured in? [1]
Volts
What is Potential Difference (P.D.)? [2]
the work done by a unit charge passing between two points in a circuit
What is P.D. measured in? [1]
Volts
What is the formula for resistance? [2]
Resistance = Voltage / Current
What is the symbol formula for Resistance? [1]
R = V / I
What is resistance? [2]
ratio of voltage to current in an appliance
What is the unit for Resistance? [1]
Ohms
Where is a Voltmeter meant to be connected? [1]
across the appliance
What’s the formula for E.M.F? [2]
volts = joules / coulomb
What’s the symbol formula for E.M.F? [1]
V = J / C
What’s is Ohm’s Law? [1]
voltage / current
What is Ohm’s Law in symbols? [1]
V / I
Why is copper used for wiring? [2]
- good electrical conductor
- cheap
What are some factors which affect resistance? [3]
- length
- cross-sectional area
- temperature
What is the relationship between length and resistance? [2]
R ∝ L
What does the relationship between length and resistance mean? [2]
- if length increases, resistance increases too
What is the relationship between temperature and resistance? [2]
- the greater the temperature, the greater the resistance
What is the relationship between the cross-sectional area of a wire and resistance? [2]
- the smaller the cross-sectional area of a wire, the greater the resistance
What are Ohmic conductors and how do their graphs look? [2]
- conductors which obey Ohm’s Law
- their I-V graph is a straight line through the origin
What are Non-Ohmic conductors and how do their graphs look? [2]
- conductors that do not obey Ohm’s Law
- their I-V graph is not a straight line and doesn’t go through the origin
What is the formula for energy? [2]
Energy = Voltage x Current x Time
What is the symbol formula for energy? [1]
E = VIT
What is the formula for power? [2]
Power = Voltage x Current
What is the symbol formula for power? [1]
P = VI
How do you work out the total resistance in a series circuit? [1]
Rₜ = R₁ + R₂ + R₃
How do you work out the E.M.F of the source in a series circuit? [2]
- sum of PD across each
- E.M.F. = V₁ + V₂ + V₃
What happens to the current if there’s a bigger resistance in a parallel circuit? [1]
- current decreases
What happens to the current in a parallel circuit when it reaches a branch point? [1]
the current splits ups
How do you work out the total resistance in a parallel circuit? [2]
1/Rₜ = 1/R₁ + 1/R₂ + …
How much voltage does each branch get in a parallel circuit? [1]
same voltage as the supply
How do I find out the total voltage in a parallel circuit? [2]
Vₜ = V₁ = V₂
What is the formula for power dissipated in a resistor? [2]
power = current² x resistance
What is the symbol formula for power dissipated in a resistor? [2]
P = I²R
