P3 - Electric circuits Flashcards
What is the motor effect
The idea that a current carrying wire in the the presence of a magnetic field will experience a force
What angle does the wire have to be to the direction of magnetic field
90 degrees, to feel the full effect of the force
What causes the force felt on a current carrying wire
The two magnetic fields interacting, pushing the wire out of the magnetic feild
What will happen to the wire if it is at an angle to the magnetic feild
It will feel less force
What do you need to know to find the direction of the force (motor effect)
The direction of the magnetic field
The direction of the current
What does fleming’s left hand rule tell you
The direction of force felt by a current carrying wire in a magnetic field
In fleming’s left hand rule, what do you match up with the direction of magnetic field
index finger (point from N to S)
In fleming’s left hand rule, what do you line up the middle finger with
The direction of current along the wire
What does the direction of the thumb tell you, in fleming’s left hand rule
The direction of the force felt by the wire
What is the formula for the size of the force felt by the current carrying wire
F = BIL
B = magnetic flux density
I = current
L = length of wire
How can you create a potential difference and current with a magnet and a wire
By moving either the wire, or the magnet through each other, a potential difference and current will be made
How can you change the direction of current in a generator
By changing the direction of the magnet (or wire), or changing the orientation of the magnet
What 3 ways can you increase the size of the potential difference and current made by a generator
Increase the strength of the magnet
Move the wire more quickly
Make more turns in the coil
Why do we need step up transformers
To minimise the energy loss over long distances
Why do we need step down transformers
To make the voltage safe for everyday use
What is the voltage in power cables
400,000 V
What is the voltage in homes
230 V
What is the first coil, the centre, and the second coil called
Primary coil, iron core, secondary core
If 10 volts goes in and 20 comes out, what happened to the ratio
The secondary coil had twice as many coils
What are the stages of a transforment
An alternating potential difference is applied across the primary coil
This causes an alternating current, which generates an alternating magnetic field which induces a field in the core
This induces a potential difference across the secondary wire, (because the magnetic field direction was alternating), and makes a current flow around the secondary coil
What do transformers change
The voltage
What is the equation for Voltage
V = IR
If the voltage stays constant and the current increases, what will happen to the resistance
It will decrease
On a VI graph, will a wire with more resistance make a steeper or shallower line
Shallower, because it requires more voltage to get a small current
Why is the line of a filament lamp on a VI graph curved down
Because as the current increases, the filament gets red hot, which increases the resistance. This means that the currents rate of increase will slow as the voltage gets increased
Why do diodes only work in one direction
Because there is a very high resistance in the reverse direction, meaning no current can flow
Why does adding resistors in parallel decrease the total resistance?
There are more routes for electrons to take between the branches, so it is easier for current to flow.
Equation linking power, current resistance
P = I^2R
In a series circuit, what happens to the voltage
The total voltage is shared by the individual components
In a series circuit, what happens to the current
It is the same everywhere
In a series circuit, what happens to the resistance
The total resistance is the sum of the resistance felt by all the components
Will components with a greater resistance have more or less voltage
More
In fleming’s left hand rule, which pole do u point at
Point from north to south
In a parallel circuit, what happens to the voltage
It is the same across all branches
In a parallel circuit, what happens to the current
It is shared between the branches
In a parallel circuit, what happens to the resistance
The more loops in the circuit, the less overall resistance there is
What is the symbol for a fuse
A box with the wire running through the middle
What is the symbol for a diode
A circle, with a right facing triangle and line, with the wire running through the middle
What is the symbol for a led
A diode with two lines coming off of it
What is the symbol for a variable resistor
A resistor with a diagonal arrow running through
What is the symbol for a light dependant resistor
A resistor in a circle with 2 arrows facing it
What is the symbol for a thermistor
A resistor with a diagonal line running through with a little flat bit at the end
As light gets more, what happens to the resistance in a light dependant resistor
It decreases
As heat gets more, what happens to the resistance in a thermistor
It decreases
