Current

Question 1

Differences between emf and pd

Answer 1

emf is two points across emf source but pd is any two points
emf: non-electrical to electrical
pd: electrical to non-electrical
emf: property of electrical source
pd: exists only if there is current flow as it represents energy transfer due to motion of charge carrier

Question 2

Why do electrons move so slowly but bulb light up quickly

Answer 2

When switch is closed, an electric field is set up almost immediately within external circuit, causing all free electrons to drift towards higher potential simultaneously. Free electrons are already present in filament of lamp whose motion are immediately responsible for lighting of lamp. As free electrons leave filament, new electrons enter and are responsible for lighting the bulb

Question 3

Characteristics of drift velocity of charge carriers

Answer 3

Speeds are distributed according to Maxwell-Boltzmann distribution.
No preferred direction for motion of charge carriers
Random velocities of charge carriers are equally likely to be positive or negative along any axis

Question 4

How does drift velocity average above zero in presence of electric field

Answer 4

Velocity of charge carriers is increased in direction opposite to applied electric field and decreased in direction of applied electric field in conductor, average velocity is now above zero

Question 5

Types of current

Answer 5

Varying dc current
Steady dc current
Sawtooth ac current
Sinusoidal ac current

Question 6

What is equation of sinusoidal alternating current

Answer 6

I = Imax sin(wt)
where w is angular frequency

Question 7

How to find root mean square value for non sinusoidal current

Answer 7

Square every value (in I/t graph)
Find mean of squared function
(area under graph for one period/period)
Root the mean value