Chapter 14-16. EM, EMI, AC Flashcards
- Define Magnetic Flux Density (B)
- Is it a Scalar or Vector Quantity?
- S.I. Unit?
- The magnetic flux density is defined as the force per unit length per unit current acting on an infinitely long current-carrying conductor placed perpendicularly to the magnetic field
B = F/(ILsin90)
- Vector
- Tesla (T)
Define Tesla (T)
The magnetic flux density of a magnetic field is said to be 1 tesla, if the force acting per unit length on an infinitely long conductor carrying a current of 1 A and placed perpendicularly to the magnetic field is 1Nm-1
Formulae for Chapter 14 and 15. EM and EMI
11 Total
- F = BILsinθ
(Fleming’s Left-Hand Rule) - Torque (τ) = NBIhbsinθ = NBIAsinθ
(since h*b = A) - Magnetic Force (F_B) = BQvsinθ
- r = mv/Bq
(Derived from Fac = F_B) - T = 2πm/BQ
(Derived from v=rω) - BQv = QE
- V = BLv
- ∅ = B⊥A
- Φ = N∅ = NB⊥A
- NBAcos(ωt)
- NBAωsin(ωt)
- Define Magnetic Flux (∅)
- Is it a Scalar or Vector quantity?
- S.I. Unit?
- The magnetic flux through a plane surface is the product of the magnetic flux density normal to rhe surface and the area of the surface
∅ = B⊥A
- Scalar
- weber (Wb)
Define weber (Wb)
There is a magnetic flux of 1 weber through a surface if a magnetic field of flux density of 1T exists perpendicularly to an area of 1m^2
1Wb = 1T * 1m^2
- Define magnetic flux linkage
2. S.I. Unit?
- The magnetic flux linkage is defined as the product of the number of turns of the coil and the magnetic flux through each turn
Φ = N∅ = NB⊥A - weber turns (Wb turns)
Define Faraday’s Law
The magnitude of the induced emf is directly proportional to the rate of change of magnetic flux linkage
Define Lenz’s Law
Lenz’s Law states that the polarity of the induced emf is such that it tends to produce a current that creates a magnetic field so as to oppose the change in magnetic flux
Strategy for answering Qualitative Qn using Faraday and Lenz’s Laws
- Identify the body where the emf or induced current is induced
- Identify the cause of the change in the magnetic flux
- Apply Farady’s Law to explain the magnitude of he induced emf/current
- Apply Lenz’s Law to explain the direction of the induced emf/current
When do we use induced emf and when do we use induced current?
Induced emf is when there is an open circuit such that current cannot flow
Induced current is when the circuit is closed
What are the formulae for a coil rotating in a magnetic field with an angular velocity of ω?
- Magnetic flux linkage
- Induced E.M.F
- NBAcos(ωt)
2. NBAωsin(ωt)
Define Alternating Current
Alternating Current occurs when charge carriers periodically reverse their direction of motion
How to find Irms or Vrms when given I-t or V-t graph?
- Square the I-t or V-t graph to get the square value
- Calculate the area under graph in one period
- Divide the area by the duration of the period to get the mean-square value
- Square root the mean-square value to get the root-mean-square value
