3.5.1 Electricity Flashcards
Equation that connects V, I and R.
V = I R
What is V, units?
Voltage, volts.
What is I, units?
Current, amps.
What is R, units?
Resistance, ohms.
Equation that connects R, ρ, L and A.
R = ρ L / A
What is ρ, units?
Resistivity, ohm metre.
What is L, units?
Length, metres.
What A, units?
Cross sectional area, metres squared.
What is the equation that connects P, I and V?
P = I V
What is P, units?
Power, watts.
What is the equation that connects P, V and R?
P = V^2 / R
What is the equation that connects P, I and R?
P = I^2 R.
What is the equation for Q, I and t?
Q = I t
What is Q, units?
Charge, coulombs.
What is t, units?
Time, seconds.
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.
P.d is referred to as what?
Voltage.
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.
An ammeter is used to measure ____?
Current.
An ammeter is always connected in ____?
Series.
What is the ammeter connected in series to?
The resistor or component.
A voltmeter is used to measure ________?
Potential difference.
A voltmeter is always connected in ____?
Parallel.
What is the voltmeter connected in parallel to?
The resistor or component.
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.
If you get measurements for wire in mm what do you do?
Convert, x10^-3.
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.
In what everyday appliances will you find a variable resistor/rheostat?
Dimmer switches, volume control.
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 sometimes referred to as?
Lost volts.
What is Ir?
P.d across internal resitor.
What is IR?
P.d across resistor.
Vout = ?
Vin x R2 / R1 + R2
What is a regular thermistor called?
Negative temperature coefficient.
What happens as temp decreases for a NTC thermistor?
Res 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?
Nope.
Resolution is what?
The smallest dectectable change by a measuring system.
What is precision?
Number of d.p.
Define potentioal diviofser circuit.
A combination of resistors in series connected across a voltage source (to produce a required pd) .
