Electricity and Magnetism / Electromagnetism and Digital Electronics

Question 1

Ferrous Materials

• Definition
• Example

Answer 1

• Attracted by magnet and can be magnetised
• iron, steel, nickel and cobalt
  (iron temporary and steel permanent)

Question 2

Non-ferrous materials

• Definition
• Example

Answer 2

• Not attracted by magnet and cannot be magnetised

- copper, silver, aluminium, wood, glass

Question 3

Electric field

Answer 3

The space or region around a charge where a unit charge experiences a force.
The direction is outward from (North) positive charge and inward into (South) negative charge

Question 4

Electric field intensity

• Definition
• Formula

Answer 4

Amount force (f) exerted by the charge on a unit charge (q) placed at a point in the field.

E = F / Q

E is the electrical field intensity in N/C

Question 5

Current (I): Rate of flow of charges in conductor

Answer 5

I = Q / t

I is the current in amperes (A),
Q is the charge in coulombs (C)
t is the time in seconds (s)

Question 6

Current

Answer 6

In circuits the current always choose the easiest path

Question 7

Ohms law

def

formula

Answer 7

Voltage across the resistor is
directly proportional to current,
V⋉ I

R = V / I
V is the voltage in volts (V),
I is the current in amperes (A) and
R is resistance in ohms (Ω)

Question 8

Voltage (potential difference)

Answer 8

Energy per unit charge

V = Energy (E) / Charge (Q)

q is the charge in coulombs (C),
V is the voltage in volts (V)
Energy is in joules (J)

Question 9

Resistance in terms of the resistivity of a resistor

fomula

Answer 9

R = p x (L / A)

R is the resistance a resistor
ρ is the resistivity of resistor in Ω
L is the length of a resistor in meters
A is the area of cross-section of a
resistor in m^2

Question 10

Voltage and Current in series vs. parallel Circuits

Answer 10

In series circuit→ the current stays the same and voltage divides
In parallel circuit → the voltage stays the same and current divides

Question 11

Resistance in series

Answer 11

R = R1 + R2 + R3

all represent resistances in Ω

Question 12

Resistance in parallel

Answer 12

1/R = 1/R1 + 1/R2 + 1/R3

all represent resistances in Ω

Question 13

Potential divider or potentiometer

Answer 13

V1 / V2 = R1 / R2

Question 14

Potential divider

V1 or V2 formula

Answer 14

V(1 or 2) = (R2 / (R1 + R2) ) x V

Question 15

Power (W)

Answer 15

P = I x V

P = I^2 x R

P = V^2 / R

Question 16

Power (J)

Answer 16

P = energy / time

Question 17

Diode def

Answer 17

Semiconductor device… current pass only in one direction, rectifier

Question 18

Transistor def

Answer 18

Semiconductor device works as a switch , collector, base, emitter

Question 19

Light dependent resistor

Answer 19

LED resistor dependant upon light, brightness increases when the resistance decreases

Question 20

Thermistor

Answer 20

Resistor depend upon temperature, temperature increase resistance decrease

Question 21

Capacitor

Answer 21

Parallel conductor with insulator in between to store charges

Question 22

Relay

Answer 22

Electromagnetic switching device

Question 23

Fleming’s RH or LH rule

Answer 23

Thumb direction of motion (Force)
Index finger direction of magnetic field lines
Second finger direction of current

Question 24

Transformer

Answer 24

Vp / Vs = np / ns

Vp and Vs are the voltages; np and ns are the number of turns in primary and secondary coils

(second formula TBA)

Power in primary coil =Power in secondary coil
Ip and Is the currents in primary and secondary coil

Question 25

E.M induction

Answer 25

Emf or current is induced in a conductor when it cuts the magnetic field lines

Question 26

a.c. generator

Answer 26

Produce current, use Fleming’s right hand rule

Question 27

d.c. motor

Answer 27

Consume current, use Fleming’s left hand rule

Question 28

Logic gates

Answer 28

AND:
only 1 outcome if both inputs are 1

NAND:
opposite of AND

OR:
only 0 outcome if both inputs are 0

NOR:
opposite of OR

NOT:
1 input and output is opposite of input

Question 29

Cathode rays

Answer 29

Stream of electrons emitted from heated metal (cathode). This process is called thermionic emission.

Question 30

CRO

Answer 30

Horizontal or y-plates for vertical movement of electron beam.
Timebase or x-plates for horizontal movement

Question 31

Emf def

Answer 31

energy needed to drive 1 unit of charge around a circuit