Electricity and magnetism

Question 1

Ferrous Materials

Answer 1

Attracted by magnet and can be magnetized

Eg. iron, steel, nickel and cobalt

Question 2

Non-ferrous materials

Answer 2

Not attracted by magnet and cannot be magnetized

e. g copper, silver, aluminum, wood, glass

Question 3

Electric field intensity

Answer 3

E is the electric field intensity in N/C

force exerted by the field on a unit
charge placed at a point around
another charge

E = f/q

Question 4

Current

=> Rate of flow of charges in a conductor

Answer 4

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 5

Current

Answer 5

In circuits the current always choose the easiest path

Question 6

Ohms law

Answer 6

Voltage across the resistor is
directly proportional to current,
V⋉ I or V/I = R

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

Question 7

Voltage

Answer 7

Energy per unit charge

V = energy / Q

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

Question 8

E.M.F - Electromotive Force

Answer 8

e.m.f. = lost volts + terminal potential difference

EMF=Ir + IR

Question 9

Resistance and resistivity

Answer 9

R = ρ x L/A
ρ is the resistivity of resistor in Ω.m

R is the resistance a resistor,
L is the length of a resistor in meters
A is the area of cross-section of a
resistor in m2

Question 10

Circuit

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

R, R1, R2 and R3 are resistances of
resistor in ohms

Question 12

Resistance in parallel

Answer 12

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

Question 13

Potential divider

Answer 13

V1/V2 = R1/R2

Question 14

Potential divider

Answer 14

V2 = (R2 / R1 + R2) X V

Question 15

Power

Answer 15

P = I X V
P = I2 X R
P = V2/R

P is the power in Watts (W)

Question 16

Power

Answer 16

P = Energy/time

The unit of energy is Joules (J)

Question 17

Transformer

Answer 17

Vp/Vs = np/ns

Vp is the voltage in primary coil,
Vs is the voltage in secondary coil
np is the no of turns in primary and
ns is the no of turns in secondary

Question 18

Transformer

Answer 18

power of primary coil = power of secondary coil

Pp = Ps
Ip x Vp = Is x Vs
Vp/Vs = Ip/Is

Ip is the current in primary coil and Is the current in secondary coil

Question 19

Cathode Rays

Answer 19

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