Sensing

Question 1

Current

Answer 1

Rate of flow of charge

Question 2

Kirchhoffs first law

Answer 2

Conservation of charge

IT = I1 + I2

Question 3

Potential difference

Answer 3

The potential energy difference per unit charge between two points
V = E / Q = W / Q

Question 4

Energy dissipated in a circuit

name and formula

Answer 4

W = VQ = VIt

Question 5

Power

Answer 5

P = E / t = IV = I^2R

Question 6

Ohms Law

Answer 6

V = IR
If this relationship holds true a conductor is ohmic. Metals are ohmic conductors, however when heated resistance increases and they become non-ohmic.

Question 7

Conductance

Answer 7

G = 1 / R = I / V

Question 8

Parallel circuits

Answer 8

Current: splits at junctions and adds to the total
EMF: total p.d. across every parallel component
Resistance: 1/RT = 1/R1 + 1/R2 etc
Conductance: Add to the total

Question 9

Series circuits

Answer 9

Current: same everywhere in the circuit
EMF: p.d. shared between components
Resistance: Adds to the total
Conductance: 1/GT = 1/G1 + 1/G2 etc

Question 10

Conductivity

Answer 10

Measure of the ability of a material to conduct irrespective of dimensions.

G = σA / L

Question 11

Resistivity

Answer 11

Measure of a materials resistance irrespective of dimensions.

R = ρL / A

Question 12

Conduction model of metals

Answer 12

Regular lattice of positive metal ions, with free (delocalised) electrons moving in random directions with varying speeds until a potential difference is applied. As a metal is heated the positive ions vibrate more and the free electrons begin to be obstructed; this is what increases resistance

Question 13

Current and drift velocity

Answer 13

I = nAve

Question 14

Insulators

Answer 14

Materials without mobile charges

Question 15

Semi-conductors

Answer 15

Materials that usually have very few mobile charges, but when heated this number increases greatly

Question 16

Thermistors

Answer 16

Resistance drops as temperature increases

This is because the heat frees more electrons

Question 17

LDR

Answer 17

Resistance drops as light intensity increases

This is because the photons free up more electrons

Question 18

Potential dividers

Answer 18

P.d. is shared proportionately to the resistance of components.

Question 19

Kirchhoffs second law

Answer 19

For any complete circuit:

EMF = the sum of all potential differences across all the resistances in the circuit

Question 20

Internal resistance

Answer 20

ε = V + Ir

V = ( -r) I + ε (can plot this as y=mx+c)