COE and DC Circuits

Question 1

What is electric current and its formula?

Answer 1

• rate of flow of electric charge
• I = Q/t

Question 2

What are the directions of v (speed), electron, current and electric field?

Answer 2

• speed of electron and electron has same direction
• current and electric field has same direction that is opposite to direction of electron

Question 3

What is the equation with drift velocity?

what do the symbols stand for?

Answer 3

I = nAvq
* I = current
* n = no. of charge carriers per m³
* A = cross-sectional area
* v = drift velocity
* q = charge on each charge carrier

Question 4

Why is power required to maintain an electric current in a metallic conductor?

Answer 4

• charged carriers slow down when they colllide with lattice ions in metal
• for charge carriers to continue moving in the same direction, force must be applied to these charges
• applying force over some displacement involves work done
• since power is rate of work done, power is required

Question 4

What is potential difference?

Answer 4

Energy dissipated per unit charge flow between two points of a circuit or across a conductor

Question 4

What is EMF?

Answer 4

electrical energy dissipated per unit charge in bringing that charge from one terminal to other via the external circuit

Question 4

How do resistance arise?

Answer 4

• resistance arise from imperfections in the crystal lattice which causes frequent scattering of drifting electrons under an electric field
• scattering is due to:
• lattice ion located some distance away from equilibrium position due to thermal vibration motion
• presence of impurity atom

Question 4

Is resistance due to drifting electrons colliding with each other?

Answer 4

No

Question 4

What is Ohm’s law?

Answer 4

For a conductor of constant temperature, the current in the conductor is directly proportional to the potential difference across it

Question 5

Is V = IR a statement of Ohm’s law?

Answer 5

No

(because in this equation R can be changing but for ohm’s law requires R to be constant)

Question 6

What is Ohm’s law in algebraic terms?

Answer 6

• I ∝ V
• I = kV
• R = V/I = constant (where k = 1/R)
• thus R need to be constant

Question 7

What is the graph if the metallic conductor obeys Ohm’s law?

Answer 7

If I-V graph is linear and passes through the origin

Question 8

What is load?

Answer 8

Resistance of any electric device

Question 9

What is the formula of internal resistance?

Answer 9

• EMF = Pd across r (internal resistance of battery) + Pd across R (resistor of external circuit)
• E = Ir + IR
• E = I (r+R)

Question 10

What is the maximum power transfer theorem?

Answer 10

A given source of emf delivers maximum power to a load when the resistance of load is equal to internal resistance of source

when r = R, maximum P transferred to R

Question 11

What is number density?

Answer 11

number of particles per unit volume

Question 12

What is charge?

Answer 12

amount of charge passing through a point = current × time for which current flows

Question 13

What is one coloumb?

Answer 13

One coloumb is the quantity of charge that flows through a point when a current of one ampere flows for one second

Question 14

What is resistance?

Answer 14

ratio of the potential difference V applied across a component to the current I passing through it

Question 15

What is ohm?

Answer 15

A resistor has a resistance of one ohm is a current of one ampere flows through it when the potential difference across it is one volt