Physics P1 - Current Electricity

What is electric current?

The flow of charge per unit time.

What is potential difference?

The energy transferred per unit charge.

What is resistance?

This is a measure of how difficult it is for charge carriers to pass through a component by the current flowing through it.

What is ohm's law?

It states that for an ohmic conductor, current is directly proportional to the potential difference across it, given that physical conditions are kept constant.

What is the graph for an ohmic conductor?

Straight line through the origin.

What is the IV graph for a semiconductor diode?

It has a forward bias, where current increases after a certain voltage. It has a backwards bias, where voltage is negative.

What is the IV graph for a filament graph?

This is a cubic graph through the origin, and the gradient decreases the further from the gradient it is.

What should you assume about ammeters?

They have zero resistance.

What should you assume about voltmeters?

Infinite resistance.

What is resistivity?

It is a measure of how easily a material conducts electricity.

What is the equation for resistivity?

Resistivity = resistance x cross-sectional area/length

What happens when the temperature of a metal conductor increases?

The resistance will increase.

Why does temperature increase cause resistance increase in conductors?

Atoms of the metal gain kinetic energy and move more, which causes charge carriers to collide with the atoms more frequently causing them to slow down, therefore current decreases and so resistance increases.

What is a thermistor?

It is a component, which causes resistance to decrease as temperature increases.

How can thermistors be used in a circuit?

Temperature sensors.

What is a superconductor?

It is a material which below a certain temperature, known as the critical temperature, has zero resistivity.

What does the critical temperature depend on?

It depends on the material it is made out of.

What are most superconductor's critical temperatures near?

Absolute zero.

What are applications of superconductors?

- Power cables; reduced energy loss through transmission.
- Strong magnetic fields; used in maglev trains and medical applications.

What is the rule for resistance in a series circuit?

Total resistance = sum of all resistances

What is the rule for resistance in a parallel circuit?

Reciprocal of total resistance = sum of reciprocals of all over resistances.

What is power?

It is the energy transferred over time.

What is the equation linking potential difference and time?

Energy transferred = potential difference x current x time

What is the rule for current in a series circuit?

Same everywhere.

What is the rule for potential difference in a series circuit?

The battery potential difference is shared across all elements in the circuit.

What is the rule for current in a parallel circuit?

The sum of the currents in each set parallel set of branches is equal to the total current.

What is the rule for potential difference in a parallel circuit?

The potential difference across each branch is the same.

What is the rule for joining cells in series?

Total voltage = sum of all voltages

What is the rule for joining identical cells in parallel?

Total voltage = voltage of cell 1 = voltage of cell 2 = ...

What is always conserved in DC circuits?

Charge and energy.

What is Kirchoff's first law?

The total current flowing into a junction is equal to the current flowing out.

What is Kirchoff's second law?

The sum of all the voltages in a series circuit is equal to the battery voltage.

What is a potential divider?

It is a circuit with several resistors in series connected across a voltage source, used to produce a required fraction of the source potential difference.

How do you make a variable potential divider?

Use a variable resistor.

What is an LDR?

It is a component which has a decreased resistance for increased light intensity.

What is internal resistance?

It is caused by electrons colliding with atoms inside the battery, therefore energy is lost before electrons even leave the battery.

What is electromotive force?

It is the energy transferred by a cell per coulomb of charge that passes through it.

What is the equation for EMF and internal resistance?

Electromotive force = current x (resistance + internal resistance)

What is lost volts?

It is the energy wasted by the cell per coulomb of charge.

What is the equation linking emf and lost volts?

EMF = terminal potential difference + lost volts