caa ac and dc

Question 1

if an electron has less than four electrons in it’s outer shell, its a ?
if it has more than four then its a?

Answer 1

conductor
Insulator

Question 2

what does a gold leaf electroscope do?

Answer 2

it deteects the charge of an item place on top. the charge will either repel or attract the needle, indicating the charge.

Question 3

obtaining charge without contact is called?

Answer 3

induction

Question 4

what type of ions are more efficient at carrying electrical current?

Answer 4

high energy, small ions

Question 5

why dont gases usually conduct very well?

Answer 5

low pressure gasses are very spread out, so it takes more energy for electrons to attract to the next ion.

Question 6

what are the two ways of controlling curent?

Answer 6

potential difference, and resistance.

Question 7

what 4 factors effect resiwstance?

Answer 7

size of wire, length of wire, type of material and its ro value, temperature of wire.

Question 8

potential difference from crushing?

Answer 8

piezo electric crystal

Question 9

potential difference from friction?

Answer 9

triboelectric effect

Question 10

potetnial difference from heat?

Answer 10

seabeck effect

Question 11

potential difference from light?

Answer 11

photo-voltaic

Question 12

what factor effect emf?

Answer 12

internal resistance, size of discharge current, the charge state of the cell.

Question 12

components of a lead acid battery?

Answer 12

positive plate, negative plate, cell connector, vent cap, cell cover, terminal posts.

Question 13

chemical in lead acid batteries?

Answer 13

lead peroxide, lead, sulfuric acid.
lead sulphate forms on positive plate.

Question 14

s.g for charged and discharged lead acid batteries?

Answer 14

1.280 sg charged, 1.150 sg discharged

Question 15

internal resistance formula

Answer 15

r=E-v / I

Question 16

faults of lead acid batteries

Answer 16

sulphation, buckling, sedimentation.

Question 17

nickel cadium battery’s checmicals?

Answer 17

nickel hydroxides on pos, cadmium on the neg, electrolyte is potassium hydroxide.

Question 18

pros of nickel cadmium batteries

Answer 18

long life, constant terminal voltage, charged and discharged at higher currents, discharged to very low voltages without damage.

Question 19

cons of nickel cadmium batteries

Answer 19

expensive, low cell voltage, thermal runaway is easier

Question 20

how does the wheatstone bridge determine an unknown resistor value?

Answer 20

a volt meter is connected in parallel between the know and unknown resistors, resistance value is figured out based on the voltage reading and the value of the variable resistor.

Question 21

points of a hysteresis curve

Answer 21

flux density, magnetising force.
opposite directional flux d and mag force

Question 22

eddy currents are increased by?

Answer 22

stronger magnetic fields, faster caging fields, thicker materials, low resistivity.

Question 23

eddy currents are decreased by?

Answer 23

weaker magnetic fields, slower changing fields, thinner materials, slotted/ laminated material, higher resistance materials, very fast changing fields.

Question 24

unit of mmf

Answer 24

ampere turns

Question 25

unit of reluctance

Answer 25

ampere turn/weber

Question 26

what is back emf

Answer 26

back emf, self inductance, is an opposite emf caused by collapsing magnetic fields that oppose current flow.

Question 27

what is armature reaction?

Answer 27

armature reaction is the distortion of the magnetic field due to the armature field being 90 to the main field.

Question 28

back emf=

Answer 28

-L * rate of change of current

Question 29

impedance in parallel

Answer 29

1/ (1/r^2+ (1/Xl - 1/Xc)^2)

Question 30

transformer loading vectors and autotransformers

Question 31

generator loading

Question 32

what is a balanced load?

Answer 32

when the phase currents are equal in magnitude and are displaced by 120 degrees.

Question 33

what is a symmetrical load?

Answer 33

when the phase voltages are equal in magnitude and displaced by 120 degrees