Electics Circuits (no internal resistance Flashcards
Define Potential Difference
The energy transferred per unit electric charge flowing through it
V = W/Q
Potential difference measure in…
Volts (V)
Define emf (electro motor force)
The maximum energy provided by a cell/ battery per unit charge passing through it
EMF is equal to..
Potential difference measured across the terminals of a battery when no charges are flowing in the circuit
Define:
Terminal potential difference
The voltage measured across the terminals of a battery when charges are flowing in a circuit
( voltmeter)
Define Current (strength)
The rate of flow of charge
(Ammeter)
Series circuit
1 pathway for current to flow
(1 loop)
Parallel circuit
More than 1 possible pathway for current to flow (branches)
Equation for :
*potential difference (v)
*energy transferred (work done) (w)
*charge (Q)
V = W/Q
V = voltage, potential difference, volts : V)
W= Joules (J)
Q= charge : Coulombs (C)
The charge that an object carries is measured in:
Coulombs (C)
One coulomb of charge represents:
Total amount of charge that 6.25 x 10^18 electrons will have
Define coulomb:
Energy transferred by large packets of electrons
The unit of potential difference (V(ext) / emf =
Volts / joules per coulomb (J.C^-1)
Why do voltmeters need to be connected in parallel?
It needs to measure the potential difference across a component
Internal resistance:
Energy is lost when charges move through the cell or battery
Internal resistance of cell/ battery is zero
No energy is dissipated per unit of charge/ per coulomb.
*the emf and terminal potential difference with therefore have same value)
Resistance of wires are negligible:
No energy is disappeared as charges move through the wires in the circuit
Define a coulomb
The amount of charge which passes a point in a conductor in one second when the strength of the current is 1 ampere
Current (I) =
Ampere (A) / coulombs per second (c.s^-1)
What does an ammeter measure?
The number of coulombs that pass by a certain point each second
Why do Ammeters need to be connected in series?
In order to measure the current AT A POINT that goes THROUGH a particular component
Equation for current, charge and time:
I = Q/ Δt
I = current : ampere (A)
Q = charge : coulombs (C)
Δt = time : seconds (s)
Define resistance:
The Ratio of the potential difference across a resistor to the current in the resistor.
What does resistance oppose?
The flow of electric charges
Define the unit of resistance:
One ohm (Ω) is equal to one volt per ampere
Microscopic description of resistance:
Resistance is caused by the energy lost as electrons scatter due to collisions with the atoms of the conductor, converting some of their kinetic energy into heat.
Factors that affect the resistance of a given material:
Temperature
Length
Thickness
As the temperature increases , the resistance increases
As the temperature increases, the atoms in a conductor vibrate more, leading to more collisions with electrons. These collisions hinder the flow of electrons causing resistance to increase)
As the length increases , the resistance increases
Electrons have to travel a greater distance, leading to more collisions with atoms along the way. More collisions mean more energy loss, resulting in higher resistance
As the thickness (width of the wire) increases , the resistance decreases
A wider wire provides more space for electrons to flow. This reduces the likelihood of collisions with atoms, allowing current to pass more easily, which lowers the resistance
Nature of wire (metal density)
At a constant temperature:
The potential difference across a conductor is DIRECTLY PROPORTIONAL to the current through that conductor
Equation for: current, potential difference and resistance
R = V/ I
R = resistance : ohms (Ω)
V = potential difference : volts (V)
I = current : (amperes) (A)
Resistance is measured in ohm
Ohm can also be described as
Volts per ampere
(V.A^_1)
Why does a battery in a circuit eventually go flat?
Charges drain energy as they move through cells/ batteries.
This energy is delivered to the components in the circuit where it is converted into different forms of energy.
Eventually the energy of the cell/ battery gets depleted. = unable to pass electrons through
State Ohm’s law:
The potential difference across a conductor is directly proportional to the current in the conductor at constant temperature.
Energy equation
W = V^2/ R (Δt)
Define Power
The rate at which work is done
The rate at which energy is transferred
Equation for Power
P = V^2/ R Δt
Define Power
The rate at which work is done or the rate at which energy is transferred
Power equation
P = W/ Δt
Energy (w) is measured in
Joules (J)
Power (P) is measured in
Watts (W)
Joules per second (J.S^-1)
Resistors in series circuit
The current is the same through each resistor
Calculate the equivalent (total) resistance of resistors connected in series:
R(s) /(ext) = R(1) + R(2) +…..
A series circuit is a potential difference DIVIDER
The total potential difference is equal to the sum of the potential differences across all the individual components that are connected in series.
Equation for :
Sum of potential difference
V (ext / s) = V(1) + V(2) + ….
Resistance in parallel
The potential difference is the same across parallel branches.
Total resistance of resistors in parallel EQUATION
1/ R(p) = 1/ R (branch 1) + 1 / R(branch 2) …
R(branch 1) : total resistance of all resistors in branch 1
R(branch 2) : total resistance of all resistors in branch 2
Parallel circuits are current dividers:
Total current in the circuit is equal to the sum of the branch circuits
Calculate the equivalent/ effective external resistance of a combined circuit (series & parallel connections)
Calculate R(p) first
Then- R(ext) by adding the series resistors
R(ext) = R(p) + R(s)
