Topic 10 - Electricity And Circuits Flashcards
In a closed circuit, if theres potenial difference in the circuit there will be a
Current
What is current?
The rate of flow of charge (or electrons) around a circuit
Unit for charge
Coulombs, C
Draw a switch circuit symbol
Closed the line goes across
Draw the circuit symbol for a cell
Draw circuit symbol for battery
Draw circuit symbol for a lamp
Draw the circuit symbol for a fuse
Draw the circuit symbol for a voltmeter
Draw the circuit symbol for an ammeter
Draw the circuit symbol for a diode
Draw the circuit symbol for a resistor
Draw the circuit symbol for a thermistor
Draw the circuit symbol for a variable resistor
Draw the circuit symbol for an LDR
Draw the cicuit symbol for an LED:
Ways a component can be connected in a circuit?
Series (same loop)
Parallel (adjacent loop)
Voltage is know as
Potenial difference
How does p.d across two components vary when connected in series and parallel?
In series, total P.D is shared between each component
In parallel circuit the P.D across each component is the same
2 resistors are connected in parallel, what can be said about their combined total resistance?
Their total resistance is less than smallest of the two indivual resistances
2 resistors are connected in series, what can be said about their total resistance?
Total combined resistance is equal to the sum of the two individual resistances.
Where must a voltmeter be placed in a circuit?
In parallel with the component that is being measured
Give an equation relating potenial difference with energy transferred and charge.
Potenial difference = energy transferred/ charge
V=E/Q
A volt can be described as..
Joule per coulomb
What is an electric current?
The rate of flow of charge
Give the equation linking charge, current and time
Q = I x t Charge = current x time Coulombs = current x time
What can be said about the value of current at any point in a single closed loop?
Current is the same at all points in a closed loop.
Factors that current in a circuit depends on?
Potential difference (V) Resistance (R)
Equation for P.D (current and resistance are known)
V = I x R
Potenial difference = resistance (ohms/A) x current (I)
What is an ammeter and where must it be connected in a circuit?
An ammeter measure current. It is placed in series with the component it is require to measured.
What happens when current reaches a junction in a circuit?
Current is conserved; the total current remains the same is split between the two branches.
How does resistance affect current in a circuit?
As total resistance of a circuit increases, the current flowing through the circuit decreases.
How can the current in a circuit be varied?
Using a variable resistor
Equation linking current and resistance
Current (A) x Resistance (ohms) = p.d (V)
V = IR
How is total resistance affected by two resistors in series?
The total resistance increases; equal to the sum of the two resistors
How is total resistance affected by two resistors in parallel?
The total resistance decreases; it is less than the resistance of the resistor with the lowest resistance.
What is an “Ohmic Conductor”? State the condition required
A conductor for which current and p.d are directly proportional
Resistance remains constant as current changes
Temperature must be constant
List four components for which resistance is not constant as current changes
Filament lamps
Diodes
Thermistors
Light dependent resistors (Ldrs)
What happens to the resistance of a filament lamp as the temperature increases? Why?
Resistance increases
Metal ions have more KE, so vibrate more, colliding more frequently with electrons as they flow through the metal
This creates more resistance to current.
What is different about current flow through a diode?
The current only flows in one direction.
Resistance is very high in the other direction, preventing current flow.
State what happens to the resistance of a thermistor as temperature increases
The thermistor resistance decreases
Give two examples of when a thermistor may be used
In a thermostat to turn a heater on below a certain temperature
In a freezer to turn on cooler when temperature is too high
State what happens to the resistance of an LDR as light intensity decreases
The LDR’s resistance increases
Give an application for a LDR
Street lamps or night lights
How do diodes work?
A diode only allows current to flow in one direction. If current is flowing the right way, the resistance is large for small voltages (up until 0,6V) then becomes very small at higher voltages
What electrical component does this graph represent?
Diode
What factors affect the enery transferred when charge flows through a component?
Amount of charge
The potenial difference across the component
Equation linking energy, current and p.d and time
Energy (J) = p.d (V) x current (A) x time (s)
E = v x I x t
Define p.d in terms of charge
The work done per unit charge
Equation relating p.d to charge
Energy transferred (J) = Charge (C) x p.d (V) E=QV
When an electrical current flows through a resistor, why does it heat up?
There are collisions between electrons and the ions in the resistors lattice. This causes a transfer of KE into thermal energy which is released into the surroudings.
How do low resistance wires reduce unwanted energy transfers?
A smaller resistance will mean there are fewer collisions, therefore less energy will be wasted through heating.
What are some advantages of the heating effect?
It is useful for appliances such as toaster or electricity fires, where the heat is the desired product.
What are some disadvantages of the heating effect?
The loss of energy as heat energy can make an appliance inefficient
If an appliance overheats it can catch fire or overheat, which could ruin the device or injure the user.
Energy transferred per second is also known as..
Power
What is power?
The rate of energy transfer, or the rate at which work is done.
Units for power
Watts, W
Equation linking power and p.d
Power (W) = current (A) x p.d (V).
Equation for power without p.d
Power (W) = current^2 (A) x resistance (ohms)
P = I^2R
Equation linking power and energy
Power (W) = energy (J) / Time(s)
Both equations linking power with resistance
P = I^2 x R P = V^2 / R
