Electricity Flashcards
What are the two types of current?
- alternating current (ac)
- direct current (dc)
Where does alternating current come from?
Mains (from a generator)
Where does direct current come from?
Batteries
What causes electricity?
The movement of electrons
What is the relative charge and atomic mass of an electron?
- charge = -1
- mass = 1/1836
What is the relative charge and atomic mass of a proton?
- charge = +1
- mass = 1
How is a negative ion formed from a neutral atom? What makes it negative?
- gain of electrons
- more electrons than protons
How is a positive ion formed from a neutral atom? What makes it positive?
- loss of electrons
- more protons than electrons
What allows a conductor to conduct electricity?
Free electrons which can move and carry a charge
What materials are conductors of electricity?
- most metals
- graphite
Why do insulators not conduct electricity?
They have very few free electrons
What is the name of the measuring device for volts?
A voltmeter
What is the name of the measuring device for amperes?
An ammeter
How does a voltmeter connect to a circuit?
Across the component
How does an ammeter connect to a circuit?
Connects directly to the circuit
What does Ohms Law state? (3)
-The current in an electrical conductor (including graphite)
- is directly proportional to the voltage across it’s ends,
- provided the temperature remains constant
The four factors that the resistance of a wire depends upon are:
- material
- length
- cross-sectional area
- temperature
The resistance of an insulator is ___ ____ the resistance of a conductor
Greater than
What is the relationship between resistance of a wire and its length
(At constant temp)
directly proportional
What is the relationship between resistance of a wire and its cross-sectional area
(At constant temp)
Inversely proportional
What is the gradient of a voltage current graph?
Resistance
Why does a filament bulb NOT obey Ohm’s Law
- It’s temperature changes
- when current flows through it
What shape would a voltage current graph be for a filament bulb?
A curve - not a straight line
What is the only non-metal conductor?
Graphite
What is another term for free electrons?
Delocalised
What is the difference between a cell and a battery?
A battery is made from two or more cells
In what direction do electrons move in an electrical circuit?
Negative to positive terminal
(Cathode to anode)
What is Conventional current?
The flow of imaginary positive charges from the anode to cathode
What way is an Ammeter always placed?
In series
What way is a Voltmeter always placed in a circuit?
In parallel
What is resistance?
The opposition to the movement of electrons
What does the term ‘series’ mean
The components have the same current but the voltage splits
State Ohm’s Law
- Voltage is proportional to current
- provided the temperature remains constant
What is the equation for Ohm’s Law?
Give units
V=IR
Voltage = current x resistance
Volts = Amperes x Ohms
V
I R
State the equation linking current and charge
Give units
Q = I x t
Charge = current x time
Coulombs = Amperes x seconds
Q
I t
State the equation linking work done, Charge and Voltage
Give units
W = QV
Work done = charge x voltage
Joules = Coulombs x Volts
W
QV
What is conventional current based on?
The plum pudding model
Which side of a cell is positive and what is its name?
Long side
Anode
Which side of a cell is negative and what is its name?
Short side
Cathode
State the equation for resistance in a series circuit
Rtotal = R1 + R2 + R3
State the equation for resistance in a parallel circuit
What do you have to do to find the final answer?
1/ Rtotal = 1/R1 + 1/R2 + 1/R3
Invert
Explain by collision theory how heat is generated by movement of charges (3)
- electrons strike positive ions in lattice
- kinetic energy converted to thermal
- positive ions heat up material
What happens to resistance as temperature increases?
Resistance increases
How many joules are in 1 KWh?
3 600 000 J
What is 1 KWh?
1000J / 1sec for 3600 sec
Or
1000J / 1sec for 1 hr
What is the equation for KWh?
KW x h = KWh
Kilowatt x hour = kilowatt hour
Why is an earth wire essential?
It can prevent electric shock / damage to an appliance along with a fuse
What is the other name for a variable resistor?
How is variable resistor displayed?
- Rheostat
- resistor with arrow diagonally through
What are the 3 wires in a three pin plug (+colour)
Where are they connected?
- live wire (brown)
- neutral wire (blue)
- earth wire (green/yellow)
- neutral wire in left hand pin
- live wire in right hand pin
- earth wire in top pin
What is the symbol for double insulation?
A square inside a square
What form of current moves in the opposite direction to conventional current?
Electron flow (cathode to anode)
What size of current flows through components in series?
What does the voltage of the supply equal?
- the same current through each component
- the sum of the voltages across the separate components
What size of voltage is observed through components in parallel?
What does the total current from the supply equal?
- the same voltage as the supply
- the sum of the currents through the components
Why does electron flow cause heat production?
Free electrons-atom collisions
Where are switches placed in a circuit?
The positive side (live side)
What is alternating current? (2)
- current that reverses direction
- periodically
