P3 - Electric Circuits Flashcards
What is electrical current?
It’s the rate of flow of electrical charge. Cannot flow if the circuit is closed.
What is p.d?
pushes the electrical charge around. Voltage (v)
What is resistance?
Anything that resists the flow of charge. Unit: Ω
What is the equation for finding the amount of charge that has flowed through a component at a given time?
Charge(C) = current (A) x time (s)
what is the formula linking current, p.d, and resistance?
V = I x R
Potential difference (V) = current (A) x resistance (ohm)
how does the length of a wire affects its resistance?
(hint: practical)
resistance increases as you increase the length of the wire
what is a linear component?
linear components have a fixed resistance. Their i-v characteristic is a straight line
what is a non-linear component?
Their resistance changes depending on the size of the current. they have a curved i-v characteristic.
what is the term i-v characteristic?
refers to a graph of how the current (I) flowing through a component changes as the p.d (v) is increased.
true or false: resistance of a component varies
true
what is a diode?
made from a semiconductor material. Let’s current flow freely in one direction but not in the other
What is an LDR?
Light dependant resistor. In darkness, the resistance is the highest. As light increases, resistance fails
What is a thermistor?
hot conditions = resistance drops
cooler conditions = resistance increases
what are sensing circuits?
LDRs and thermistors can be used
can be used to turn on or increase the power of the components, depending the condition they are in
Where does an electrical current transfer energy from?
a power supply
how do charges transfer energy against a component?
they pass through it by doing work against the resistance of a component
What is the formula which relates to p.d between 2 points, the work done, either on or by a charge?
potential difference = work done (J/energy transferred) ÷ charge
What is power measured in?
Watts, W = 1J/s
what is the equation for calculating the power transfer in a circuit device in a given time?
power (W) = energy (J) ÷ time (s)
P = E ÷ T
what is the equation for calculating power using voltage and current?
power (W) = p.d (V) x current (A)
P = VI
what is the equation for using resistance and current to calculate the power?
power (W) = current² (A²) x resistance (Ω)
P = I²R
What is power rating?
it is the rate at which energy is transferred
What is the p.d of a series circuit?
the p.d of supply is shared between the various components
V(total) = V1 + V2 + V3
What is the current in a series circuit?
each charge has to flow through all the components to get round the circuit. So all the same current flows through all parts of circuit
I1 = I2 = I3
What is the resistance in a series circuit?
the net resistance of a series circuit is just the sum of the individual resistances
R = R1 + R2 + R3
What is the p.d in a parallel circuit?
is the same across all branches, as each component is directly connected to the power source
V1 = V2 = V3
What is the current in a parallel circuit?
shared between branches
loops that have greater resistance take a lower share of current
Itotal = I1 + I2 + I3
what is the resistance in a parallel circuit?
the more resistance components added in a parallel circuit, the lower the resistance as the current has multiple paths to flow through, reducing the opposition
from which pole does the magnetic lines go to?
north to south
what are like poles and unlike poles?
like poles repel
unlike poles attract
where is the magnetic field the strongest?
at the poles
how does a compass show the direction of magnetic fields?
there is a tiny bar magnet inside a compass. The north pole of this magnet is attracted to the south pole of any other magnet close. Hence, the compass points in the direction on the magnetic field it is in.
what are permanent magnets?
permanent magnets produce their own field
what are induced magnets?
are magnetic materials that turn into magnets when they’re put into a magnetic field. When u take the field away, they lose their magnetisation and return to normal
what happens when a current flows through a wire?
a magnetic field is created around the wire. The field is made up of concentric circles perpendicular to the wire.
the larger the current / or closer to the wire u are, stronger the field is
why do you use the right hand thumb rule for?
to work out the direction of the field around a wire
clockwise / anticlockwise
what is a solenoid?
A coil of wire
it’s strong and uniform
How can you increase the strength of a magnetic field in a wire?
You can increase the strength of the magnetic field by wrapping the wire into a coil called solenoid.
There are fields around each turn
How can you increase the strength of a solenoid?
(4)
increasing the current through the coil
increasing the number of turns but keeping the length the same
decreasing the cross-sectional area of a solenoid
add a block of iron (becomes induced)
Why are electromagnets useful?
you can switch them on or off, and because they’re so quick to turn on or off as they create a varying force.
what did electromagnets lead to the use of?
electromagnetic relay
What is the motor effect?
when a current-carrying conductor (e.g wire) is put near a permanent magnet, the 2 magnetic fields interact with each other. This causes a force to be exerted on both the wire and magnet. this is the MOTOR EFFECT
what is required to experience the force of the motor effect?
the wire has to be at 90 degrees to the magnetic field.
what is fleming’s left hand rule?
it’s used to tell you the direction of the force on a current carrying conductor that is at right angles to a magnetic field
how do you use fleming’s left hand rule?
point ur First Finger in the direction of the magnetic Field (north/south)
seCond finger in the direction of Current
ur thuMb will be the Motion (force)
what three things is the force acting on a conductor at 90 to a mag field proportional to?
magnetic flux density
the size of the current through the conductor
length of the conductor
what is the equation to calculate the force when it’s at 90
force N = magentic flux density (T) x current (A) x length of conductor (m)
What are step-up transformers?
steps up the potential difference. More turns on the secondary coil that the primary coil
(power stations)
What are step-down transformers?
Steps p.d down, more turns on primary coil than secondary coil
(consumer end)
are transformers 100% effiecient? and what can we use to show this
true
input power is equal to the output power
p.d across primary x current in primary = p.d across secondary coil x current in secondary coil
when are transformers used?
when transmitting electricity across the country via the national grid
explain the d.c motor
the force is
explain a use of electric motors
in a blender to make the blades move
