P2.3 Currents in electrical circuits Flashcards
What happens when 2 electrically charged objects are brought together?
they exert a force on each other
When will 2 objects attract?
if the 2 objects carry different types of charge (have opposite electric charge +, -)
When will 2 objects repel?
When the 2 objects carry the same type of charge ( +,+ or -, -)
What materials can electrical charges move easily through?
good conductors- eg metals
What is electric current?
a flow of electric charge
What is the size of electric current?
the rate of flow of electric charge
in the equation
I = Q (divided by) t
what do the letters stand for and what are the units?
I- current in amps (A)
Q- charge in coulombs (C)
t-time (s)
When does more charge pass around a circuit?
when a bigger current flows
What is potential difference (voltage) ?
the energy transferred per coulomb of charge that passes between 2 points in a circuit
What is resistance?
Anything in the circuit which slows the current down
The greater the resistance across a component…….
the smaller the current that flows
What is the potential difference between 2 points in an electrical circuit?
the work done (energy transferred) per coulomb of charge that passes between the points
(amount of energy that is transferred per unit of charge)
In the equation
V = W (divided by) Q
what does each letter stand for and what are the units?
V- potential difference (V)
W- work done (J)
Q- charge in coulombs (C)
What is another word for voltage?
potential difference (p.d)
Describe a thermistor and its uses
- is a temperature dependent resistor
- in hot conditions the resistance drops, so more current
- in cool conditions the resistance goes up, so less current
- make useful temperature detectors eg- thermostats + car engine temperature sensors
Describe light dependent resistors (LDR) and its uses
- dependent on INTENSITY of light
- bright light, resistance falls- more current
- darkness, resistance increases- less current
- useful as automatic night lights, out door lighting and burglar detectors
What are current-potential difference graphs used to show?
how the current through a component varies with the potential difference across it
What happens when certain insulating materials are rubbed against each other?
They become electrically charged
because negatively charged electrons are rubbed off one material and on to the other
The material that gains electrons becomes negatively charged and the material that loses electrons is left with an equal positive charge
The electrically charged materials attract smaller objects near them
Describe the current-potential difference graph for a resistor
(eg LDR or thermistor)
The current through a resistor is directly proportional to the P.D
Describe the current-potential difference graph for a resistor
(eg LDR or thermistor)
The current through a resistor is directly proportional to the P.D
Why in an LDR the more light, the more current?
as with more light there is less resistance
this is because light allows electrons to have energy and flow
Why in a thermistor the higher the temperature, the greater the current?
as the higher the temperature, the less resistance
This is because the temperature causes the electrons to have more energy and move due to increased kinetic energy of particles
Describe the current-potential difference graph for a filament lamp
a curve
as the temperature of the filament increases and resistance increases
In a filament bulb, why does increasing the temperature increase the resistance?
with a higher temperature, the ions in the conductor vibrate more which makes it harder for the electrons to get through the resistor, meaning the resistance increases
How can the resistance of a component be found?
by measuring the current through, and potential difference across the component
In the equation
V= I x R
what do each of the letters stand for and what are the units?
V- potential difference (V)
I- current (A)
R- resistance in ohms
On a current-potential difference graph, the steeper the gradient….
the lower the resistance
On a current-potential difference graph, what does it mean if the graph curves?
the resistance is changing
The current through a component depends on its ….
resistance
The greater the resistance in a component, the ……….. the current through the component
smaller
What are the rules for components connected in series?
total resistance is the sum of resistance of each component
same current through each component
total P.D of the supply is shared between the components
What are the rules for components connected to parallel?
The P.D across each component is the same
Total current through circuit is the sum of the currents through separate components.
What happens if you remove or disconnect one of the components from a series circuit?
The circuit is broken and all the components stop working
There is a bigger potential difference in a series circuit when…
more cells are in the circuit
In a parallel circuit, why do identical bulbs have the same brightness?
Because in parallel circuits, the potential difference is the same across all components
In a series circuit, why do identical bulbs not have the same brightness?
As in series circuits, potential difference is shared across all components
Ammeters are always connected in….
series
even in parallel circuits
Voltmeters are always connected in…
parallel with a component
even in a series circuit
Why is it important that ammeters have very low resistance?
So the ammeter affects the current as little as possible
What does an ammeter do?
Measures the current in amps flowing through the components
In a circuit, where can an ammeter be placed?
anywhere in series in the main circuit but never in parallel like the voltmeter
What does a voltmeter do?
it measures the potential difference in volts across a component
Where is a voltmeter placed in a circuit?
must be placed in parallel around the component under test
NOT around the variable resistor or battery
Describe the current through a diode
current through a diode flows in 1 direction only. The diode has a very high resistance in the reverse direction
Why is there an increasing use of LED lighting?
as they use a much smaller current than other forms of lighting
When does an LED emit light?
When a current flows through it in the forward direction
What do LEDs stand for?
light emitting diodes
What causes a driver in a car to become charged?
the drivers clothing and the car seat rub together
the friction causes electrons to transfer from either the seat to the driver or from the driver to the seat
Why does the resistance of the metal filament inside the bulb increase as the potential difference across the bulb increases?
exam answer-
metals contain free electrons
as temperature of the filament increases, ions vibrate faster
electrons collide more frequently with the ions
so velocity of electrons decreases
Why does a diode cause the trace on a oscilloscope screen to change?
diode has a large resistance in the reverse direction
so it stops the current to flow in that direction
Why does electric charge flow more easily through copper
because copper has a low resistance
In simple terms, why does the resistance of a bulb increase as the potential difference across the bulb increase
as the temperature of the bulb increases
When obtaining data to plot a current-potential difference graph, why is a variable resistor used?
to obtain a range of p.d values
