Physics Module 4 Electric Circuits

Question 1

1. Charge

Answer 1

Q. Electric charge is the physical property of matter that causes it to experience a force when placed in an electromagnetic field. There are two-types of electric charges; positive and negative (commonly carried by protons and electrons respectively).

Question 2

2. Elementary Charge

Answer 2

The elementary charge is ± 1.6 x 10-19 C.

Question 3

3. Coulomb

Answer 3

C. Unit of charge.

Question 4

4. Electric Current

Answer 4

I. Rate of flow of charge. I = ΔQ / Δt.

Question 5

5. Ampere

Answer 5

A. Amp. Unit of current. The current is 1 ampere when 1 coulomb flows in 1 second. Coulomb per second.

Question 6

6. Quantise

Answer 6

Form into ‘quanta’. Restrict the number of possible values of (a quantity) or states of (a system) so that certain variables can assume only certain discrete magnitudes. For example, photons.

Question 7

7. Discrete

Answer 7

Discrete in science is the opposite of continuous: something that is separate; distinct; individual. For example in quantum theory, discrete may refer to discrete quanta.

Question 8

8. Conventional Current

Answer 8

Conventional Current flows from + to –. Conventional means ‘based on or in accordance with what is generally done or believed’.

Question 9

9. Electron Flow

Answer 9

Electrons flow from – to +.

Question 10

10. Kirchhoff’s First Law

Answer 10

Sum of or total current into a junction equals the sum of or total current out of a junction. Charge is conserved.

Question 11

11. Conservation

Answer 11

The principle by which the total value of a physical quantity or parameter (such as energy, mass, linear or angular momentum) remains constant in a system which is not subject to external influence.

Question 12

12. Mean Drift Velocity

Answer 12

v. The average displacement/distance travelled of the electrons along a wire per second. They move slowly in one direction through the (copper) lattice when there is a p.d. and collide constantly/in short distance with the lattice; measured in ms-1.

Question 13

13. Number Density of Charge Carriers

Answer 13

n. The number of electrons per unit volume, m-3.

Question 14

14. Conductors, Semiconductors and Insulators

Answer 14

Conductors, semiconductors and insulators are distinguished by their number densities. Conductors ~ 1028 m-3; semiconductors ~ 1017 m-3; insulators ~ 0 m-3

Question 15

15. P.d

Answer 15

V. P.d or potential difference is the work done per unit charge, measured in volts. Energy is transferred from electrical into other forms. V = W / Q.

Question 16

16. Volt

Answer 16

V. Unit of voltage or p.d. or e.m.f. The voltage is 1 volt when energy of 1 J is transferred per coulomb of charge. Joule per coulomb.

Question 17

17. E.m.f

Answer 17

E. E.m.f or electromotive force is the work done per unit charge, measured in volts. Energy is transferred from other forms into electrical. E = W / Q.

Question 18

18. Resistance

Answer 18

R. Voltage per unit current. R = V / I.

Question 19

19. Ohm

Answer 19

Ω. Unit of resistance. The resistance is 1Ω when a 1 V supply pushes a current of 1 A. Volt per ampere.

Question 20

20. Ohm’s Law

Answer 20

The voltage across a conductor is proportional to the current flowing through it; as long as other conditions like temperature remains constant. Shown by a straight line through the origin on an IV graph.

Question 21

21. Ohmic and Non-Ohmic

Answer 21

A component that obeys Ohm’s Law is ohmic. A component that does not obey Ohm’s Law is non- ohmic.

Question 22

22. Resistivity

Answer 22

ρ. Resistivity = ( Resistance x Cross Sectional Area ) / Length. Ω m.
Electrical resistance of a conductor of unit cross-sectional area and unit length. R = ρ L / A.

Question 23

23. Temperature

Answer 23

T. A measure of the average kinetic energy of the particles in a system. Adding heat to a system causes its temperature to rise. Temperatures are commonly measured in the Kelvin or Celsius scales.

Question 24

24. NTC

Answer 24

‘Negative Temperature Coefficient’. An increase in temperature causes a decrease in another variable such as resistance.

Question 25

25. Power

Answer 25

P. Work done per unit time. Measured in watts,W or joules per second, Js-1 .P=IV =I2 R=V2 /R.

Question 26

26. Kilowatt-Hour

Answer 26

kWh. A unit of (electrical) energy equal to 3 600 000 joules. 1 kWh is transferred when a 1 kW appliance is on for 1 hour.

Question 27

27. Series

Answer 27

A closed circuit in which the current follows on one path.

Question 28

28. Parallel

Answer 28

A closed circuit is divided into two or more paths.

Question 29

29. Kirchhoff’s Second Law

Answer 29

The sum of, or total, e.m.f.s into a loop equals the sum of, or total, p.d.s / voltages out of a loop.

Question 30

30. Resistance of Resistors in Series

Answer 30

RTOTAL = R1 + R2 + R3 + … Recall all resistors in series have the same current.

Question 31

31. Resistance of Resistors in Parallel

Answer 31

1/RTOTAL = 1/R1 + 1/R2 + 1/R3 + … Recall all resistors in a parallel loop have the same total voltage.

Question 32

32. Internal Resistance

Answer 32

r. Some energy is transferred into thermal energy / lost as heat in driving charge through the battery. It behaves as if it has an internal resistance. There is a voltage drop across / decrease in voltage from the battery when a current is drawn from it. Lost volts per unit current. E = I(R + r) ; E = V + I r.

Question 33

33. Terminal P.d

Answer 33

V. Terminal pd = e.m.f. – voltage lost to internal resistance. V = E – I r.

Question 34

34. ‘Lost Volts’

Answer 34

v. Voltage lost due to internal resistance. E.m.f. – Terminal pd. v = Ir, where r is internal resistance.

Question 35

35. Potential Divider Equation

Answer 35

VOUT = R2 / (R1 + R2) and V1/V2 = R1 / R2.

Question 36

36. Sensor

Answer 36

A device which detects or measures a physical property and records, indicates, or otherwise responds to it. The sensitivity of a sensor is the change of the output divided by the change of the input.