Current Electricity Flashcards
What is current electricity?
The result of electrical charge on the move. In metal wires this charge is carried by the negative electrons which we call free electrons.
What is conventional current direction?
Before discovering the electron it was thought that the current was caused by positive charges on the move from the positive to negative terminal of the power supply. We now know that current is caused by negative electron flow from the negative to positive terminal
How to know conductors and insulators?
Conductors are metals and non-metals are insulators
How do free electrons work with conductors and insulators?
Metals have a regular lattice structure of ions and a ‘cloud’ of delocalised electrons. If a voltage, the free electron will drift in the direction of the positive terminal. Non-metals lack free electrons, they are locked in the bonding process, so can’t conduct
What is the rule when measuring current in a series circuit?
The current is always the same. Also the current leaving the power supply equals the current returning to it so current is not used up as it flows
What is the rule when measuring current in a parallel circuit?
The current will divide at junctions and recombine. But it is always conserved
What is current?
The rate of flow of charge (The coulombs per second)
Equation triangle for charge (Q)
Q
I T
What is one coulomb?
Charge passing any point in a circuit when a steady current of 1 ampere flow for 1 second
What is one ampere?
Current flowing in a conductor when a charge of one coulomb past any point in one second
What does the potential difference do in a circuit? (Voltage)
It is the source of energy for electrons to move. When a complete circuit is made the electrons will try to flow from the higher energy level to the lower one. As the voltage increases the energy gained by the electrons will increase and hence the current flow will also increase.
What is the rule for measuring voltage in a series circuit?
Adding together the voltage of each component. E.g. V1 + V2 = V3
What is the rule when measuring voltage in a parallel circuit?
The voltages across the components are the same and equal the voltage supply
What are the properties of an ammeter and voltmeter?
Ammeter is connected in series and must have a very low resistance to the flow of electric current.
Voltmeter is connected in parallel and must have a very high resistance to the flow of electric current.
What circuit is related to Ohm’s law?
Using a piece of wire and a variable resistor to change to voltage and hence the current flowing through it
Why include a switch in an Ohm’s law circuit?
Prevents the wire from heating up between readings, which is what could happen if the current was to flow continuously through it.
What does Ohm’s law state?
The current through a metal wire is directly proportional to the voltage across it as long as temperature and physical conditions remains constant.
What is the equation triangle for Ohm’s law?
V
I R
What does each unit mega, kilo, milli and micro mean?
Mega - 1,000,000
Kilo - 1,000
Milli - 0.001
Micro - 0.000001
How to find resistance in a series circuit?
Adding each resistor value together
What is the rule with resistors in parallel?
When two equal resistors are added together in parallel their combined resistance is half of one of them
How to add resistors in parallel?
R1 X R2
———
R1 + R2
How to find total resistance in triple parallel?
Find one third of one of the resistors
What is short circuiting?
It a connecting wire is put in between a lamp the lamp will go out as the wire has a very low resistance so the current simply bypasses the lamp. It can be dangerous as it reduces the resistance of the circuit and can allow a very large current to flow
