3.1 - Electrical Quantities Flashcards
Tell me about the electric charge
Some particles have an electric charge. For example, the electron has a negative charge.
In SI units, electric charge is measured in coulombs
What’s the amount of charge on s single electron
-1.6 x 10^19 C
How many electrons is is 1 coulomb
- 25 x 10^18
6. 25x10^18 x 1.6 x 10^-19 = 1 C
How must total charge be conserved
The chargers on fundamental particles such as electrons are fixed properties of these particles, it is impossible to create or destroy charge - the total charge must always be conserved
What’s current
If electric charge moves, it’s referred to as an electric current
The strict definition of current is the rate of movement of charge
Or rate of flow of charge
We can say it flows as it’s a physical movement of billions of tiny charged particles
When does electric current occur
When a charged particle, which is free to move, experienced an electric force, if it can move it will be accelerated by the force. This movement of charge forms the electric current
Any source of electrical energy can create an electric force in order to produce a current
In a circuit, a cell causes the electric force, experienced by the negative conduction electrons so they move through the metal - they’re attracted to the positive snore of the cell
What are most electric currents made from
Most electric circuits are made from metal wiring in which there are electrons that are free to move
There conduction electrons then form the current.
Which way is conventional current
From positive to negative (from left to right) but in reality it goes from negative to positive as electrons are negative
What’s the SI unit for electric current
Ampere, A
How can current be calculated
Current = charge passing a point/ time for that charge to pass
I = Q/t
What is 1 ampere equal to
One ampere is the movement of one coulomb of charge per second
How do we calculate charge
Q = I x t
How can we observe charge flow
We can monitor small movements of charge, to see how they form a current, using a hanging ball that will conduct electricity
A suspended ball can carry small numbers of electrons across a high voltage gap, and tha current is measured using a spot galvanometer
The high voltage set up across the air gap between the metal plates encourages negative electrons to went to move towards the positive side
The hanging ball is painted with conducting paint and swings backwards and forwards across the gap, ferrying a small quantity of electrons from one metal plate to the other each time
We can measure the small movement of charge on a very sensitive ammeter, if we time the period of oscillation of the shuttling ball and the tiny current, we can calculate how many electrons pass across each journey - if the ball is moving too fast to be timed by the eye, we can use a STROBOSCOPE to measure the frequency of oscillations
What are ionic charge characters
If the circuit is more unusual, there may be other charged particles, charge carriers, which can move to from an electric current
Eg free aluminium ions (charge carriers) that can move through the liquid as an electric current - still observe the conservation of charge.
What’s the charge on a proton
It’s the same magnitude as an electron but positive
1.6 x 10^-19
Question - what would be the charg on an iron ion (III), Fe^3+
Three electrons have been lost, so the net charge is that of the ions three excess protons
3 x 1.6 x 10^19 C
Define charge
Charge is a fundamental property of some particles. It is the cause of the electromagnetic force, and it is a basic aspect of describing electrical effects
What is one coulomb
One coulomb is the quantity of charge that passes a point in a conductor per second when one ampere of current is flowing in the conductor, the amount of charge on a single electron is -1.6x10^-19
Define the electric current
It’s the rate of flow of charge
What is 1 ampere
It’s the movement of one coulomb of charge per second
How can an electrical circuit be useful
It acts as a means to transfer energy usefully, the circuit must have at least one component that can supply electrical energy, it will also have components that convert this electrical energy into other forms, and st least one of these forms of energy will be useful in its purpose
Defin voltage
It’s a measure of the amount a component transfers per unit of charge passing through it
How can voltage be calculated
Voltage = energy transferred / charge passing
V = E/Q
What’s an electromotive force
For a supply voltage, a component which is putting electrical energy into a circuit - the correct term for the voltage is electromotive force or emf
If a cell supplies 1 J per coulomb, it has an emf of 1 volt