Chapter 28: Sources of Magnetic fields

Question 1

What is the law of Biot and Savart i.t.o I and dL

Answer 1

B = (μ0/4π) (I dLxrHAT)/r^2

Question 2

What is the law of Biot and Savart i.t.o v,q and r

Answer 2

B = (μ0/4π) (qv x rHAT)/r^2

Question 3

When is magnetic field due to a current element zero

Answer 3

when:
v //r
dL//r

Question 4

what is the eq for the magnetic fireld ( magnitude only) of a long conductor, i.t.o r a and I

Answer 4

B = (μ0 I /2πr)
note that this is the same as the amperes law derivation when we let r = R

Question 5

what si the force bertwen parallel striaght current carrying conductors when they are

a) I’s in the same direction
b) I’s in opposite directions

Answer 5

a) Like implies attract

b) opposite impleis repel

Question 6

What is the formulation and result of total magnetic flux around a magnet or for htta matter any other thing that proiduces magnetic fields such as a current caryring wire

Answer 6

Φ B = ∫ (closed path) B . dA = 0 always
NOTE THIS IS NOT HE B.dL FROM AMPERE’S LAW, THIS IS A PURELY MATHEMATICAL DERIVATION

think gauss law has Φ electric = Qenc / Ɛo, but we do not have discrete Qenc for mag netic sources as no magnetic monopoles exist. thus the Qenc equivalent is always zero

Question 7

Ampere’s law in words and eq

Answer 7

∫ (closed path) B . dL = μ0 I(enclosed)

Ampere’s Law states that for any closed loop path, the dot product of the length elementsand the magnetic field (both as vectors) is equal to the permeability times the electric current enclosed in the loop.

Question 8

Principle of superposition of magnetic fields

Answer 8

The total magnetic field caused by several moving charges is the vector
sum of the fields caused by the individual charges

Question 9

is magnetic flux a scalar or vector quanity

Answer 9

flux is a scalar quantity

result of dot porduct between B and dA, NOT dL

Question 10

unit of magnetisc flux

Answer 10

weber

Tesla/m^2