Elecrtricity Flashcards
Define current and its units
The rate of flow of charge measured in Amps
Define potential difference and its units
The work done moving a unit charge between two points in a circuit measured in Volts
Define resistance
How difficult it is to move a current through an appliance
What is an ohmic conductor?
a conductor which obeys ohm’s law meaning that current is directly proportional to p.d. Providing physical conditions (temperature) to remain constant
What does the gradient of the current-p.d. Graph represent?
It is the rate of change of p.d. With respect to current, not 1/R
What does a graph look like for a filament lamp?
As current increases resistance increases so it is like an S-shape for IV and reverse s shape for VI
Why does the current increasing on the filament lamp cause an increase in resistance?
As current flows through the lamp, electrical energy is converted to heat energy so the metal ion vibrate with increased amplitude. This impedes the movement of electrons through the lamp as they collide with the ions (resistance has increased).
What is a diode and what does the graph look like?
Appliance which only allows current to flow in one direction for IV
what is a thermistor and what does the graph look like?
semi-conductor which depends on temperature and when temp increases resistance decreases.
Why is it assumed that voltmeters have infinite resistance?
current takes the path of least resistance, so when the voltmeter is applied in parallel no current will flow through it and all the current will flow through the appliance.
What is resistivity? And state its units
The resistance of a 1m length with a 1m^2 cross-sectional area. Measured in Ohm-metres. It is a property of a metal
What is a superconductor
A material with 0 resistivity at or below a critical temperature. The critical temperature is an inherent property of the material.
Give examples of the uses of superconductors.
Reduction of energy loss in transmission of electrical power.
Production of strong magnetic fields.
Electronic circuits that work very fast due to no resistance to slow them down.
how does the current vary between each component of a series circuit?
The current through all of the components is the same so the current does not vary
If 5 identical cells are arranged in parallel what is the voltage in the circuit?
The voltage of one of the cells.
If 5 identical cells are arranged in series what is the voltage provided in the circuit?
the sum of all the cells’ voltages.
Is the current in parallel components the same?
According to kirchhoff’s 2nd law each branch of a parallel circuit can have different currents through.
What is kirchhoff’s first law?
All of the current going into a junction is equal to the current leaving the junction.
What is kirchhoff’s second law?
For any path (loop) of a circuit, the sum of all of the potential differences must equal to the total emf of the circuit.
What is power?
The rate of energy tranfer
What is the purpose of a potential divider?
To provide a variable p.d. Or provide a constant specific p.d.
What is emf?
The electromotive force - the electrical energy transferred by a power supply per unit charge.
If internal resistance is negligible what can be assumed about the emf and the terminal p.d.?
That they are the same
What is lost volts?
The energy wasted per coulomb overcoming the internal resistance.
Conservation of energy in emf
energy per coulomb transferred in load resistance
+
Energy per coulomb wasted in internal resistance
Make the emf equation into y=mx+c form
V=emf - Ir
Equation associated with potential dividers
Vout = R2/R1+R2 x Vin(supplied p.d.)
