Electromagnetism: Circuits / Electromagnetic Radiation Flashcards
What happens when you charge an RC circuit with a capacitor?
Current will flow onto the capacitor, potential difference will increase
What happens when you discharge an RC circuit with a capacitor?
The current flows off of the capacitor, potential difference decreases
What is the time taken for a capacitor to charge dependent on?
The resistance of the resistor and capacitance of the capacitor
What affect does increasing the resistance have on charging on discharging time?
It increases because less current flows at the start of the process.
What affect does increasing the capacitance have on charging on discharging time?
It increases as more charge is stored on the capacitor/
What happens to charging and discharging time when you increase the supply voltage?
It increases as it will take longer time for capacitor to reach higher voltage.
What is the time constant when a capacitor is charging?
The time taken to increase the charge stored to 63% of the difference between initial and full charge.
What is the time constant when a capacitor is discharging?
The time taken for the capacitor to discharge to 37% of its initial charge.
In an RC circuit, when can an uncharged capacitor be considered to be fully charged?
After a time approximately equal to 5t. (5 times the time constant)
What does a large time constant mean?
That a capacitor will charge or discharge slowly.
Draw the diagram for Capacitors in AC Circuits
Remember:
- Multimeter set to ac current
- Resistor with multimeter set to ac voltage around it
- Signal generator
What is the results of plotting a graph of current vs frequency? (Capacitor in AC circuit)
A straight line from Y-axis
:. Shows that current in resistor remains constant with frequency
When a resistor is replaced with a capacitor and the experiment is repeated, what does the graph now look like? (Current vs Frequency)
Diagonal line from origin
What is Capacitive reactance, Xc?
The opposite of a capacitor to changing current
How do you find Capacitance from the capacitive reactance equation?
C = 1/
2(pi) f Xc
When does electromagnetic induction take place?
When a moving magnetic field cuts a conductor to create an e.m.f across it
What does the magnitude of the e.m.f depend on?
SLS
- Strength of the magnetic field
- Length of wire cutting the magnetic field
- Speed of movement
:. Greater they are, the greater induced e.m.f
What happens if the conductor moves parallel with the magnetic field or is stationary? (Inductors in DC circuits)
There will be no e.m.f provided
What does an inductor consist of?
coil of wire often wrapped around an iron core, which increases its effectiveness.
What does Lenz’s Law state?
The induced e.m.f always opposes the change in current which causes it.
What is the inductance, L, of an inductor?
- 1 H when e.m.f of one colt is induced across ends of inductor
- current in inductor changed at 1A per second
Where is energy stored around in the magnetic field?
Around a current-carrying inductor.
What is inductance, L, measured in?
Henries (H)
What happens when an inductor is suddenly turned off?
The magnetic field rapidly collapses, producing a large back EMF
The large back EMF can create a spark across the open contacts of the switch.
Sketch a circuit for an Inductor in AC circuits
Remember:
- Signal generator (• ~ •)
- Voltmeter around signal generator
- Iron-cored inductor
- Resistor next to inductor
- Ammeter
What does a graph of current vs 1/frequency give?
A diagonal line from origin
What is inductive reactance?
The opposition of an inductor to changing current.
How are magnetism and electricity mutually related?
- changing magnetic field is able to generate an electric field
- changing electric field is able to generate a magnetic field.
How is the electromagnetic wave formed?
When an electric field combines with a magnetic field.
