Electric current is the rate of flow of charge and is measured in amperes (amps)
Potential difference is the work done moving a unit charge between 2 points in a circuit, represented by V = W / Q
Resistance is how difficult it is for current to flow through an appliance. A component has a resistance of 1Ω if 1A flows through it when a p.d of 1V is applied across it, represented by R = V / I
An ohmic conductor is a conductor that obeys Ohm’s law, meaning that current is directly proportional to potential difference providing physical conditions (such as temperature) remain constant
Current in a circuit can be measured with an ammeter connected in series with the component
Potential difference across a component can be measured using a voltmeter connected in parallel across the component being measured
The gradient of a current-potential difference graph represents the rate of change of current with respect to voltage, not the same as 1/R
A graph represents an ohmic conductor if the line has a constant gradient and passes through the origin, showing that voltage is directly proportional to current
A graph with higher resistance requires a higher voltage for the same change in current compared to a graph with lower resistance
A curve representing a filament lamp shows that as current increases, resistance also increases. A big increase in voltage produces only a small increase in current
Increasing current on a filament lamp causes an increase in resistance as electrical energy is converted to heat energy, causing metal ions to vibrate and impede electron movement
A diode is an appliance that only allows current to flow in one direction
Voltmeters are assumed to have infinite resistance unless stated otherwise, ensuring all current flows through the appliance being measured
An ammeter is assumed to have zero resistance unless stated otherwise, so there is no potential difference across it and it does not affect the circuit
A Light Dependent Resistor (LDR) is a semiconductor sensitive to light, with resistance decreasing as light intensity increases
A thermistor works similarly to an LDR, but as temperature increases, resistance decreases due to its negative temperature coefficient
Resistivity is the resistance of a 1m cylinder with a cross-sectional area of 1m^2, an inherent property of a material represented by ρ = RA/L
An experiment to determine the resistivity of a metal involves measuring the resistance, length, and cross-sectional area of a wire, then calculating resistivity using the formula ρ = RA/L
A superconductor is a material with zero resistivityat or below a critical temperature, which is an inherent property of the material
In a series circuit, the total resistance is the sum of the individual resistances of each component
If 6 cells, each with a voltage of 5V, are arranged in parallel, the voltage in the circuit is 5V
If 6 cells, each with a voltage of 5V, are arranged in series, the total voltage provided to the circuit is 30V (5V x 6)
In a series circuit, the current through all components is the same
In parallel components of a circuit, the current can vary as each branch can have different currents according to Kirchhoff’s first law
Kirchhoff’s first law states that all the current going into a junction is equal to the current leaving the junction
Kirchhoff’s second law states that for any path (loop) of a circuit, the sum of all potential differences must equal the total emf of the circuit
If two cells in a series circuit are connected negative to negative, their emf will cancel out, resulting in a total emf of ε total = ε 1 - ε 2
Power is defined as the rate of energy transfer
The equation for power in terms of current and voltage is Power = Current x Voltage (P = IV)
The purpose of a potential divider is to provide either a variable potential difference or a constant specific potential difference
In a circuit with a cell providing 12V to resistors of 6Ω and 7Ω in series, the voltage across the 7Ω resistor is 6.5V
EMF (Electromotive force) is the electrical energy transferred by a power supply per unit charge
Two applications of superconductors are power cables to reduce energy loss during transmission and strong magnetic fields for applications like maglev trains and medical uses
The total resistance of a parallel arrangement of 3Ω, 7Ω, and 9Ω resistors is 1.7 Ω
RP06 - Method:
Set up the apparatus as shown in the diagram.
With the switch open, record the reading V on the voltmeter.
Set the variable resistor to its maximum value, close the switch and record V and the reading I on the ammeter.
Open the switch between readings.
Decrease the resistance of the variable resistor and repeat this, obtaining pairs of readings of V and I over the widest possible range.
Rearranging for y = mx + c:
Ɛ = I(R + r)
Ɛ = IR + Ir
As V = IR; Ɛ = V + Ir
Ɛ - Ir = V
V = -rI + Ɛ
where:
y = V
x = I
gradient is -r
y-intercept is Ɛ
Explain what is meant by resonance
Idea that (at resonance) frequency of forced vibrations equals natural/resonant frequency
Idea that amplitude (of vibrations/oscillations) is at a maximum
State what is meant by the emf (electromotive force) of a battery.
Work done in moving 1 C of charge the whole way around a circuit
Explain how the law of conservation of energy applies in this circuit. You should consider the movement of one coulomb of charge around the circuit.
(1 C of) the charge gains ε J on passing through cell
ε = IR1 + IR2 + Ir
Explain, in terms of electron movement, why the resistance of the filament lamp changes as the voltage changes as shown in Figure 3.
As the voltage increasesmore electrons move through the wire per second
More collisions per second between the conduction electrons and the latticeions
The rate of vibration of the lattice ions increases causing a greater number of collisions per second causing increased resistance