Electricity Part 1 Flashcards
To make an electric current pass round a circuit:
1) The circuit must be complete/closed.
2) A source of potential difference in the circuit
Define ‘Electrical current’
Electrical current is the rate of flow charge (in the wire or component)
Electrical current is due to…
….the flow of charged paticles, called charge carriers.
2 Examples of charge carriers?
1) In conducting metals, the charge carriers are delocalised electrons .
2) In a salt solution, the charge carriers would be the charged ions.
What is conventional current?
Conventional current describes the flow of current from the positive terminal to the negative terminal.
What is electron flow?
Electron flow is the opposite to the conventional current and flows from the negative terminal to the positive terminal (this is the direction of flow in reality)
What is the unit of charge?
Coulombs (C)
What is the unit of current?
Amperes (A)
What is 1 Coulomb defined as?
1 Coulomb is defined as the amount of charge that passes a fixed point in 1s if the current is 1A.
What is the equation to calculate charge flow in a circuit?
Q = It [ ΔQ = ΔI x Δt ]
Δ = Change in... Q = Charge (in C - coulombs) I = Current (in A - amperes) t = Time (in s - seconds)
How to calculate number of electrons passing a fixed point along the wire each second?
Total Charge (passing a fixed point each second) / Charge of an electron = Number of electrons passing a fixed point each second)
e.g. If 1C of charge is flowing per second, the number of electrons flowing is equal to 1C / 1.6 x 10^-19 C = 6.25 x 10^18 electrons. Because 1C is carried each second (1s), 1A of current flows. So 1A is due to 6.25 x 10^18 electrons.
What device is used to measure the current?
An ammeter
What electrical terms can be used to describe materials?
1) Conductors
2) Insulators
3) Semiconductors
What is an electrical conductor?
An (electrical) conductor is a material that allows the flow of charge carriers through it towards the positive terminal, when a voltage is applied.
What is an electrical insulator?
An (electrical) insulator is a material that does not allow the flow of charge carriers through it, when a voltage is applied (the electrons remain bound to the atoms).
What is a semiconductor?
A semiconductor, is a material that conducts current but only partly. The conductivity of a semiconductor is somewhere between that of an insulator (no conductivity) and a conductor (full conductivity).
What is a pure semiconductor and what is it also referred to as?
*You do not need to know what a dopant specie is.
A pure semiconductor, AKA an ‘intrinsic semiconductor’ is a semiconductor, that does not include any dopant species (traces of impurity elements). The numer of charge carriers is therefore determined by the properties of the materials itslef than the amount of impurities.
For a pure semiconductor, what happens when you increase the temperature?
When you increase the temperature, the resistance across it decreases, as the number of charge carriers flowing through increases.
When a battery is not in a complete circuit…
…it has the potential to transfer energy from its chemical store to the electrical store of the charge carriers.
When a battery is in a complete circuit…
…each electron passing through a circuit component does work to pass through that component and therefore transfers some or all of its energy (that has been transferred from the chemical store of the battery).
The work done by an electron is therefore equal to…
The work done by an electron = the loss of energy by an electron
The potential difference/voltage across a component can be defined as?
The work done per unit charge across the component.
If work W is done, when charge Q flows through a component the pd across the component, V, is given by?
V = W/Q
V = Potential Difference (V) W = Work done (J) Q = Charge (C)
What is the electromotive force (emf) of a source of electricity?
The emf is defined as the electrical energy produced per unit charge passing the source.
What is the unit of emf?
The unit of emf is also the volt (V).
What is the equation to calculate electrical power, linking together current and voltage?
P = IV
P = Power (W) I = Current (A) V = Potential Differencce (V)
Define Electrical Resistance (of a component)
Electrical resistance of a component is a measure of how difficult it is to get a current to flow through it.