P4 - Electric Circuits Flashcards
List the 2 types of circuits
Series and Parallel
define static charge
electrical charge that is unable to flow
what is static charge caused by
friction which leads to electrons being transferred to another body
what can generate static electricity
practical
Vandegraff generator
Give one use of static electricity
- painting metal (e.g. cars)
- photocopier
- insecticides
Give the danger of static electricity
sparks can be caused when a charged object is discharged by being earthed
define current
the rate of flow of electrical charge in a circuit
equation for current (A)
I = Q / t
Amps = Coulombs / seconds
current = charge / time
define electrical charge
a property of matter that causes it to experience a force in an electric field
Does current add up or is it the same across components in a series circuit?
Current is the same across all components in a series circuit.
Does current add up or is it the same across components in a parallel circuit?
Current adds up in a parallel circuit.
define potential difference
in terms of electrical potential
measure of difference in electric potential energy between 2 points
define potential difference
in terms of force
measure of force or “push” P.D. gives the current
P.D. - potential difference
equation for potential difference
using coulombs
V = W / Q
Volts = Joules / Coulombs
voltage = energy / charge
Does voltage add up or is it the same across components in a series circuit?
Voltage adds up in a series circuit
Does voltage add up or is it the same across components in a parallel circuit?
Voltage is the same across all components in a parallel circuit.
Why does voltage add up in a series circuit?
Work done by the battery on the charge (coulombs) to “push” it must always equal the work done on all the components, otherwise energy would be lost
work done - energy transferred buckets example
define resistance
measure of how difficult it is for electrons to move in an electrical circuit
what 4 factors affect resistance, explain why they cause more collisions
- material - density and structure
- thickness - less space
- length - longer
- temperature - more vibrations
formula for Ohm’s law
V = IR
V = AΩ
voltage = current * resistance
define ohmic conductor
a conductor or component that adheres to Ohm’s law
Describe the relationship between current and voltage in a fixed resistor
The current of the fixed resistor (at constant temp) is directly proportional to the voltage across it. Ohmic conductor
x = y
Describe the relationship between current and voltage in a filament bulb
The lamp’s resistance increases as temperature increases. The current through lamp increases but starts to plateau as voltage increases, not diretly proportinal. Non-Ohmic conductor
x = y3
Describe the relationship between current and voltage in a diode
Current can only flow in one direction because if the voltage would be negative current is 0.
x = log y + c
describe how a thermistor works
in terms of temperature
A thermistor has a high resistance when it is cold and a low resistance when it is hot.
like the opposite of a regular condutor in terms of temp
describe how a LDR works
in terms of light
An LDR has a high resistance when light intensity is low and a low resistance when light intensity is high
The rule for resistance in a series circuit.
Resistance adds up in a series circuit
RT = R1 + R2
The rule for resistance in a parallel circuit.
Resistance is smaller than the smallest resistor.
Resistance decreases when adding more parallel connections to a circuit
The rule for resistance in a series circuit - WHY does it happen?
The voltage across each resistor is shared.
The rule for resistance in a parallel circuit - WHY does it happen?
The total voltage is constant across each resistor, so adding a resistor increases the total current. R = V / I, so if the voltage is constant, increasing the current will result in a lower resistance.
define direct current
Current that only flows in one direction
Define alternating current
Current that flows in 2 directions (forwards and backwards) and is constantly switching direction
