ELECTRICITY AS Flashcards
Define a potential divider circuit.
a set of resistors connected in series with a source of p.d across them.
Define the e.m.f of a cell.
The amount of energy transferred from chemical energy to electrical energy per 1 C of charge that moves through the cell.
Define electric current.
The rate of flow of charge.
Define 1 Volt.
1 volt is the potential difference between 2 points when 1 Joule of work is done to move a charge of 1 coulomb between those points.
Definition of 1 ohm.
The resistance of a component when 1 A of current flows through it when 1 V is applied across it.
Define resistivity.
The resistance of a material with a cross-sectional area of 1 m^2 and a length of 1m
Explain, in reference to electrons and metallic structure, why resistance increases for a metal when the temperature is increased.
Increasing the temperature means:
-positive ions have more energy
-so they vibrate with greater amplitude
-and so there are more frequent collisions between positive ions and electons
-causing greater resistance to the flow of electrons
Explain, in reference to electrons, why the resistance of a thermistor decreases as the temperature increases.
As the temperature increases,
- energy of the semiconductor increases
- so more electrons are released into the lattice
- more charge carriers available to carry a greater current for the same voltage
- resistance decreases
A diode allows current to flow only in one direction. What is this direction called?
Forward bias
State 2 applications of superconductors and explain why they are superior to traditional conductors in these applications.
- superconducting transmission wires - superconductors have 0 resistance below or at the critical temperature, so no energy losses to Joule heating.
- maglev trains -
superconductors can carry a huge amount of current without overheating, so they can act as really strong electromagnets.
What are the current limitations of using superconductors?
- they must be cooled below the critical temperature, which is expensive as liquid helium or liquid nitrogen is required.
Define what is meant by a superconducting material.
- A material that has zero resistivity below a critical temperature.
Define power.
The rate of energy transfer per unit time
A series circuit consists of a 4V cell and 2 resistors of value 2 and 6 ohms, connected in series.
Explain why the total power dissipated across both resistors must equal the power of the cell.
- Power is the rate of energy transfer per unit time, and energy must be conserved
- so each second, the total energy dissipated by the resistors must = total energy transferred by the cell
State Ohm’s Law.
- the potential difference across a conductor is directly proportional to the current flowing through it, provided all physical conditions remain constant.
