baseline year 11

e = q x v

energy transferred in joules = charge in coulombs x potential difference in volts

q = i x t

charge in coulombs = current in ampere x time

v = i x r

potential difference in volts = current in ampere x resistance in ohms

cell

battery

open switch

voltmeter

ammeter

lamp

describe the basic structure of an atom (positions, relative masses and relative charges of protons, neutrons and electrons)

an atom consists of a small, dense nucleus at the centre containing protons (charge +1, relative mass 1) and neutrons (charge 0, relative mass 1), surrounding the nucleus are electrons (charge –1, relative mass ≈0) in energy levels (shells), the nucleus makes up nearly all the mass, while electrons occupy most of the volume

brightness of identical lamps in circuits

in series circuits, current is the same through each lamp, but the potential difference is shared, so each lamp gets less energy per coulomb, making them dimmer whereas in parallel circuits each lamp gets the full potential difference of the cell, so they shine equally bright and usually brighter than in series

lamps in circuits

in series circuits more lamps mean the total resistance increases, current decreases, and all lamps become dimmer whereas in parallel circuits adding more lamps provides extra paths; each lamp still gets full potential difference, so brightness stays the same, but total current from the supply increases

cells in circuits

in series circuits, their voltages add, increasing the potential difference and making lamps brighter whereas in parallel circuits potential difference stays the same but they last longer as current is shared

switches in circuits

in series circuits all must be closed for current to flow (like a safety system) whereas in parallel circuits closing any one switch completes the circuit, giving multiple control points

describe how to measure voltage

measured using a voltmeter, which must be connected in parallel across the component being measured, so it measures the energy transferred per coulomb of charge through that component

define the term ‘potential difference’

energy transferred per unit charge when charge moves between two points in a circuit, measured in volts (V) where 1 V = 1 joule per coulomb (1 J/C)

describe how to measure current

current is measured using an ammeter, which is always connected in series in the circuit so the same current flows through it as through the component

describe the conditions needed to produce an electric current

for an electric current to flow, there must be a closed (complete) circuit so charges can move continuously, and a source of potential difference (e.g., a cell or battery) to provide the energy that drives the charges around the circuit

describe the behaviour of current at a junction

at a junction in a circuit, the total current entering equals the total current leaving, as charge is conserved, current splits between branches in proportion to their resistance but never disappears or is created

explain the link between the potential difference (voltage) across a battery or a component, the charge passing through it and the amount of energy transferred

the potential difference across a battery or component tells you how much energy is transferred to or from each coulomb of charge that passes through, a higher potential difference means each unit of charge gains or loses more energy

explain the link between electric current and electric charge

current is the rate of flow of electric charge, a larger current means more charge passes a point in the circuit each second

explain electric current in metals in terms of electrons

in metals, current is carried by delocalised (free) electrons in the metal lattice, when a potential difference is applied, these negatively charged electrons drift through the metal, producing an electric current

explain the link between resistance and current in a circuit

resistance opposes the flow of charge, for a given potential difference, a higher resistance means a smaller current, while a lower resistance allows a larger current

resistance when two resistors are connected in a series circuit

resistances add: the total resistance is larger because charge must pass through each resistor in turn

resistance when two resistors are connected in a parallel circuit

the total resistance is less than the smallest resistor, because current has multiple paths to flow through

explain the design and construction of series circuits for testing and measuring

series circuits are used for testing because the same current flows through all components, making it easy to compare how potential difference changes across different resistors, components like ammeters are placed in series, while voltmeters are connected in parallel to measure potential difference without altering the current

explain how current changes with potential difference in fixed resistors

for a fixed resistor at constant temperature, current is directly proportional to potential difference, this produces a straight-line graph through the origin, showing constant resistance

explain how current and resistance change with potential difference in filament lamps

in a filament lamp, as potential difference increases, current increases but not proportionally, the filament gets hotter, causing resistance to increase, so the current rises more slowly, the graph is a curve that gets shallower at higher voltages

explain how current and resistance change with potential difference in diodes, including light-emitting diodes (LEDs)

a diode only allows significant current in one direction (forward bias). In forward bias, current stays very small until a threshold voltage is reached, then increases rapidly, in reverse bias, current is almost zero, LEDs behave the same, but they also emit light when current flows forward

describe how the resistance of a light-dependent resistor (LDR) varies with changing light intensity

an LDR’s resistance decreases as light intensity increases. In bright light it has low resistance, while in darkness it has very high resistance

describe how the resistance of a thermistor varies with changing temperature (negative temperature coefficient only)

in an NTC thermistor, resistance decreases as temperature increases, at low temperatures resistance is high, and at higher temperatures it is much lower

describe the use of diodes

used to ensure current flows in one direction e.g in rectifiers for power supplies

uses of LEDs

used as indicators and in display lighting

uses of LDRS

used in light sensitive circuits such as automatic streetlights or camera sensors

use of thermistors

used in temperature sensors, thermostats and electronic circuits for temperature control