Electricity Flashcards
Electric current
Is a flow of electrical charge (electrons).
When will electrical charge flow?
Only when the circuit is closed, so there is a potential difference. The unit for current is ampere A.
Potential difference
1 volt tells us that 1 j of energy is transferred for each coulomb of charge that moves through the circuit.
Resistance
Electrons collide with atoms in the conductor, energy is transferred to other stores such as thermal. Unit ohm
The current flowing through a component depends on the…..
Potential difference across it and the resistance of the component.
The greater the resistance across a component…
The smaller the current that flows.
The size of the current is the…
Rate of flow of charge. Charge flow(Q)= current(l) x t(time, seconds)
More charge passes around the circuit when a…
Larger current flows.
Formula for potential difference
Potential difference(V)= Current(A) x Resistance(ohm)
V=IR
The ammeter
Measure the current in amps flowing through the test wire. Must be placed in series
The resistance of ohmic conductors(e.g. wire or resistor)…
doesn’t change with the current. At a constant temperature, the current flowing through is directly proportional to the potential difference across it.
The resistance of some resistors and components….
Does change (diode or filament lamp)
Filament lamp
Some energy is transferred the thermal energy store of the filament, which is designed to heat up. Resistance increase with temperature, so as the current increases, the resistance increases also.
Diodes
Resistance depends on the direction of the current. In reverse direction the resistance is very high.
LDR
Light dependent resistor. The resistance depends on the intensity of light. In bright light the resistance falls in darkness the resistance is highest.
Uses of LDR
Automatic night lights, outdoor lighting and burglar detectors.
Thermistor
Is a temperature dependent resistor. In hot conditions the resistance drops in cool conditions the resistance goes up.
Uses of thermistor
Useful temperature detectors, such as car engine temperature sensors and electronic thermostats.
If you remove one component in a series circuit….
The circuit is broken and all the components stop.
Potential difference in series circuit
The total pd of the supply is shared between various components. The pd round a series circuit always add up to equal the source pd.
Current in the series circuit
The current is the same in all components. Current is determined by total pd divided by total resistance.
Resistance in series circuit
Total resistance is sum of the resistance of all the components. Because by adding a resistor, two resistors have to share the total pd.
(Series circuit) The pd accord each resistor is lower, so the current…
Through each resistor is also lower. In s. circuit current is the same everywhere so the total current in the circuit is reduced.
(Series) The bigger a component’s resistance…
the bigger its share of the total pd is.
Cell potential difference add up
There is a bigger pd when more cells are in series, if they are all connected the same way.
If you remove one of the components…
it will hardly affect the others at all.
(Parallel) Potential difference is….
the same across all the components.
(Parallel) Current is…
shared between branches.
(Parallel) Adding a resistor…
reduces the total resistance.
The current flows from…
negative end of the cell to the positive end. However, it is drawn opposite direction.
Electrons are carrying….
energy from the cell and pass the energy to the components in circuit such as lamp.
When electrons return to…
the positive end of the cell, they are carrying less energy than when they left the negative end.
Series circuit properties
- convectional current
- no branches
- current can flows only in one path
- current is always the same all the way around
Electrical charge is measured in….
coulombs(c)
Current of 1 A = 1 c of charge flowing per second.
The cell has a store of…
chemical energy, transferred to electrical energy carried by electrons.
Battery
Two or more cells are connected together.
Resistance tells the…
p.d. required to drive a current through component.
