L8: Electromagnetism & Induction Flashcards
Magnetic Flux Definition
Magnetic Flux (Φ) (with units Weber) is defined as the number of of lines of force flowing outward from a magnet’s north pole. 1 Weber = 1x10^8 lines of force.
What is an Electromagnet (what makes up an Electromagnet)
Electric current in a conductor always has an associated magnetic field resulting in an electromagnet
How is an Induced Current formed
When magnetic flux moves, the motion of magnetic lines of force cutting across a conductor perpendicularly, forces its free electrons to move across a closed circuit, forming an induced current.
What does more current and more turns of a coil in a solenoid result in
More current and more turns on the coil (also called solenoid) produce a stronger magnetic field.
How is Induced Voltage formed
When magnetic flux cuts a conductor that is an open circuit a voltage is induced at two ends of the conductor, called an induced voltage or back emf or counter emf
What is Lenz’s Law
Lenz’s Law states that the direction of induced current (or polarity of induced voltage) must be such that it will oppose the action that produced it
What can be done using Faraday’s Law
What is self-inductance
The induction caused by an alternating current is called self-inductance or simply inductance
Self Induced Voltage value and units
Henry Defintion
1 Henry is the amount of inductance that allows 1 volt to be induced when the current changes at the rate of 1 ampere per second.
Equation for Energy stored in an Inductor (in Joules)
How is energy supplied by the volatge source
The energy is supplied by the voltage source, which can do the work of producing induced voltage when the flux moves and cuts a conductor
When and how does Mutual Inductance occur
Mutual Inductance (Lm) occurs when alternating current flowing through one conductor creates a changing magnetic field which induces a voltage in the original current carrying conductor. Unit is still called Henry.
How can Mutual Inductance between two coils be calculated
What makes up a Transformer
- A transformer has two or more windings with mutual inductance
- The primary winding is connected to an AC power source
- The secondary winding is connected to the load
- Primary current Ip induces a secondary voltage Vs, which produces current in secondary load RL.
- Voltage can be stepped-up or stepped-down
What is the Voltage Ratio for a transformer
What is the Current Ratio for a transformer
Equation for the Efficiency of a Transformer
How can coils in series be calculated when there is no mutual inductance
How can coils in parallel be calculated when there is no mutual inductance
How can coils in series be calculated when there is mutual inductance
How can coils in parallel be calculated when there is mutual inductance
When is and isnt there induced voltage in a DC circuit
What is the L/R Constant and in how many time constants does the inductor current reach its full value
The transient response of a series RL circuit iss measured in terms of the ratio L/R (where R is in ohms, and L is in Henrys), called L/R Time Constant, which is the time for a change of 63.2% in the current flowing through the inductor (whether increasing or decreasing).
In five time constants, the inductor current reaches its full value (or reduces to zero).
What are the two graphs showing L/R Time Constant
