Chapter 2: Sensing

Question 1

What is an electric current?

Answer 1

The flow of charged particles.

Question 2

What is the equation for the current of an electron/ion beam?

Answer 2

I=nq

current = no of particles per second x charge of particle

Question 3

what is the equation for electric current (and charge and time)?

Answer 3

Q=It

charge = current x time

Question 4

equation for p.d. (given charge and energy)

Answer 4

V=E/Q

p.d. = potential energy difference / charge

Question 5

equation for p.d. (given current and resistance)

Answer 5

V = IR
(pd = current x resistance)

Question 6

three equations for power

Answer 6

P=IV=I^2R=V^2/R

Question 7

What is conductance?

Answer 7

the current for a given pd

Question 8

equation for conductance

Answer 8

G = I/V

Question 9

what is resistance?

Answer 9

The pd required for a given current

Question 10

equation for resistance

Answer 10

R = V/I

Question 11

relation between conductance and resistance?

Answer 11

G=1/R ; R=1/G

They are reciprocal quantities

Question 12

State Ohm’s Law

Answer 12

For an ohmic conductor, in constant external conditions, V=IR

Question 13

Is a filament lamp ohmic? Why?

Answer 13

NO!!! Because its temperature does not remain constant! I/V graph looks like an “f”

Question 14

What is a diode?

Answer 14

A semiconducting component which only allows current to flow in one direction.

Question 15

What adds up in series?

Answer 15

Resistances and voltages

Question 16

What adds up in parallel?

Answer 16

Conductances and currents

Question 17

What is emf? (1 - relating to charge)

Answer 17

Electromotive force - the electrical energy supplied to each charge by the chemical reaction in the battery.

Question 18

What is emf (2 - relating to current)

Answer 18

The terminal voltage when there is no current drawn.

Question 19

emf equations:

Answer 19

V = e - Ir = e - v
e = I(R+r) = V + v

Question 20

What is the potential divider equation?

Answer 20

V_1 = V_c x (R_1/R_1+R_2)

Question 21

What is internal resistance?

Answer 21

The resistance to electrical current by the atoms in the cell.

Question 22

What is Kirchoff’s First Law?

Answer 22

The total current entering a junction is equal to the total current leaving a junction.

Question 23

What is Kirchoff’s Second Law?

Answer 23

The total emf around a series circuit is equal to the the sum of the potential differences across each component.