Electricity Flashcards
What equation connects V, I and R
V = I R
What equation connects R, ρ, L and A
R = ρ L / A
What equation connects P, I and V?
P = I V
What is P, units?
Power, watts
What equation connects P, V and R?
P = V^2 / R
What equation connects P, I and R?
P = I^2 R
What equation connects Q, I and t?
Q = I t
What is Q, units?
Charge, coulombs
From which end of the battery does the current flow?
Negative to positive
What does the exam board call the flow of electrons from neg to pos?
Conventional current
To make the electrons flow they have to flow to a ____ potential?
Lower
If you subtract the lower potential from the higher potential, what do you get?
Potential difference
The greater the voltage of a battery the _____ the current in a circuit?
Bigger
Something that causes difficulty in electrons flowing down a wire is called a _____?
Resistance
What is Ohm’s law?
The current flowing through a metallic conductor is directly proportional to the potential difference applied across it at a constant temp
V is directly proportional to _?
I
What is an Ammeter used to measure?
Current
What is an Ammeter always connected in?
Series
What is a Voltmeter used to measure?
Potential difference
What is a voltmeter always connected in?
Parallel
What is the definition of potential difference?
The potential difference between two points is the amount of energy transformed when one coulomb of charge is moved between the two points
What is the equation that connects W, Q and V?
W = Q V
In a series circuit the current in that particular circuit will be the ____ at every point in the circuit.
Same
In a series circuit the p.d across each resistor is ____?
Different
In a series circuit the p.d across each resistor is ____?
Different
What does the p.d all add up to in a circuit?
The battery voltage
In a series circuit V = __________?
V1 + V2 + V3`
In a parallel circuit the p.d across each branch in that particular circuit will be ____?
Same
In a parallel circuit the current in each branch may be _____?
Different
In a parallel circuit all the currents add up to the ________?
Supply Current
In parallel I =
I1 + I2 + I3
What is Kirchoff’s first law?
At any junction in a circuit the sum of the current flowing into the junction is equal to the sum of the current flowing away from it
What is Kirchoff’s second law?
In any complete loop of a circuit the sum of the sum of p.d’s equals the source p.d
In a series circuit what does Rtotal = ?
R1 + R2 + R3
In a parallel circuit what does 1/Rtotal = ?
1/R1 + 1/R2 + 1/R3
What is the equation that connects W, Q and V?
W = Q V
What is W, unit?
Work done, joules
What is the equation that connects W, P and t?
W = P t
When a current flows through a circuit some energy is transformed into ____?
Heat
When 2+ resistors are connected in series the total p.d is _____ between them
Divided
In a series circuit the largest resistor has the _______ p.d across it
Largest
In a series circuit the individual p.ds are the ____ as the power supply
Same
What does the current/voltage graph look like for a resistor?
Straight line through origin to the right, directly proportional
What does the current/voltage graph look like for a filament lamp?
S shape, to the right, intersecting origin
What does the current/voltage graph look like for a diode?
Flat then curved up in the upper right quadrant
What is the quantity that describes how restive a material is?
Resistivity
What does EMF stand for?
Electromotive force
Define EMF
The E.M.F of a cell is the voltage across the terminals of a cell when no current is flowing through it
What is the internal resistance (r)?
The resistance of the cell itself
How is internal resistance represented in a circuit diagram?
As a circle with r in it around the cell
Define electric current
The rate of flow of charge in a wire or component
What is a superconductor?
A wire or device that is made of a material that has 0 resistivity and below a critical temp
When would a superconductor lose its superconductivity?
If it’s temp is raised above critical temp
What are superconductors used to make?
High power electromagnets, used in MRI scanners and particle accelerators
What components can we see in potential divider circuits?
Variable resistors, thermistors, LDRs
What can we use potential divider circuits for?
Control of light levels, control of temp
Define terminal p.d.
T.P.D is the voltage that a cell has when current is flowing through it and an external resistor
What is the equation connecting ℰ, I, R and r?
ℰ = I (R + r)
What is ℰ, units?
EMF, J/C
What is the expanded form of ℰ = I (R + r)?
ℰ = IR + Ir
What is Ir?
P.d across internal resitor
What is Ir sometimes referred to as?
Lost volts
Vout = ?
Vin x R2 / R1 + R2
What is a regular thermistor called?
Negative temperature coefficient
What happens as temp decreases for a NTC thermistor?
Resistance increases
Why would we use a steel core for cables?
Increase mechanical strength
P.d is proportional to what?
R
Sum of p.d = ?
EMF
As light decreases LDR resistance …?
Increases
More power dissipates in what circuits, why?
Parallel, smallest R
Is the coulomb an SI unit?
No
Resolution is what?
The smallest dectectable change by a measuring system
What is precision?
Number of d.p
Define potential divider circuit
A combination of resistors in series connected across a voltage source (to produce a required pd)
