Chapter 4 – Electric Circuits
4.1 – Electrical Charges and Fields
Some insulating materials become charged when rubbed together
Electrons are transferred when objects become charged :
A material that becomes positively charged has lost electrons
A material that becomes negatively charged has gained electrons
When brought together, like charges repel whilst unlike charges attract
The force between two charged objects is a non-contact force
4.2 – Current and Charge
A battery consists of two or
more cells connected together
The size of an electric current
is the rate of flow of charge
Q
I=
t
I – the current in amps (A)
Q – the charge in coulombs (C)
T – the time in seconds (s)
4.3 – Potential Difference and Resistance
energy transferred (E)
V ( Potential Difference)=
charge(Q)
potential difference (V )
R ( Resistance ) =
current ( I )
Ohm’s law states that the current through a resistor at constant temperature is directly
proportional to the potential difference across the resistor
Reversing the potential difference across a resistor reverses the current through it
4.4 – Component Characteristics
V
The resistance of a component is R=
I
A filament lamp’s resistance increases if the filament’s temperature increases
A diode’s forward resistance is low, and its reverse resistance is high
A thermistor’s resistance decreases if its temperature increases
The resistance of a Light Dependent Resistor (LDR) decreases if the light intensity on it increases
4.5 – Series Circuits
The current is the same in each component
The total potential difference is shared between the components
Adding their resistances together gives the total resistance
For cells in series, acting in the same direction, the total potential difference is the sum of their
individual potential differences
4.1 – Electrical Charges and Fields
Some insulating materials become charged when rubbed together
Electrons are transferred when objects become charged :
A material that becomes positively charged has lost electrons
A material that becomes negatively charged has gained electrons
When brought together, like charges repel whilst unlike charges attract
The force between two charged objects is a non-contact force
4.2 – Current and Charge
A battery consists of two or
more cells connected together
The size of an electric current
is the rate of flow of charge
Q
I=
t
I – the current in amps (A)
Q – the charge in coulombs (C)
T – the time in seconds (s)
4.3 – Potential Difference and Resistance
energy transferred (E)
V ( Potential Difference)=
charge(Q)
potential difference (V )
R ( Resistance ) =
current ( I )
Ohm’s law states that the current through a resistor at constant temperature is directly
proportional to the potential difference across the resistor
Reversing the potential difference across a resistor reverses the current through it
4.4 – Component Characteristics
V
The resistance of a component is R=
I
A filament lamp’s resistance increases if the filament’s temperature increases
A diode’s forward resistance is low, and its reverse resistance is high
A thermistor’s resistance decreases if its temperature increases
The resistance of a Light Dependent Resistor (LDR) decreases if the light intensity on it increases
4.5 – Series Circuits
The current is the same in each component
The total potential difference is shared between the components
Adding their resistances together gives the total resistance
For cells in series, acting in the same direction, the total potential difference is the sum of their
individual potential differences
