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electricity Flashcards

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1
Q

which is positive and which is negative; cathode and anode?

A

cathode - negative

anode - positive

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2
Q

what is electro magnetic induction

A

a change in magnetic field induces an emf that induces current

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3
Q

how is magnetic flux measured

A

weber

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4
Q

what is fardays law of Electromagnetic induction

A

magnitude of induced emf is proportional to the rate of change of flux or E <× Ø1 - Ø 2 / t

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5
Q

what is a magnetic field

A

region where an attractive repulsive force is felt

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6
Q

in what direction do magnetic force lines point

A

north to south

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7
Q

what is an electromagnet

A

current carrying conductor

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8
Q

what is a solenoid

A

a coil whose length is linger than its radius

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9
Q

how do you make a solenoid stronger

A

place a magnetic core in it

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10
Q

what direction is a magnetic north pole

A

anti clockwise

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11
Q

what direction is a magnetic south pole

A

clockwise

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12
Q

what will a current carrying conductor experience in a magnetic field

A

a force perpendicular to current flow and perpendicular to magnetic field

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13
Q

what is conventional current direction

A

postive to negative

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14
Q

what happens if a current carrying wire enters a magnetic field parallel to magnetic flow direction

A

no force acts on it

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15
Q

what happens if a current carrying coil is placed in a magnetic field

A

it turns

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16
Q

what is a characteristic of a thermistor

A

resistence will drop dramatically at a certain temperature

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17
Q

what are the two main types of capacitors

A

an electrilytic capacitor and a parallel plate capacitor

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18
Q

what does dielectric mean

A

non conductive

19
Q

what are 3 factors affecting capacitance in a parallel plate capacitor

A

distance between plates, permitivity of dielectric material, area of overlap

20
Q

what is lenzs law?

A

the direction of current caused by electromagnetic induction will be opposite to the direction of the force causing it

21
Q

how do you demonstrate faradays law?

A
22
Q

what is the purpose of a transformer

A

to increase or decrease alternating voltage

23
Q

what is the principle operation of a transformer

A
  1. the input voltage (Vin) in the first (or primary) coil creates an alternating current there, which then creates a changing magnetic field in the core.
  2. The secondary coil is inside this changing magnetic field and so it creates an emf in the secondary coil (Vout)
    The voltage can either be increased (a step-up transformer) or reduced (stepped down).
  3. This is controlled by the relative number of turns in the primary (Np) and the secondary (Ns).
24
Q

what is alternating current

A

current that reverses direction over a set period of time

25
Q

describe an experiment to show how resistance of an LDR varies with incident light

A

connect LDR to ohmeter, shine light with verying distances and observe change in resistance on ohmeter

26
Q

what is rectification

A

conversion of a.c. ro d.c

27
Q

what semiconductor is used for rectofication

A

diode

28
Q

why is high voltage used to transport electicity efficiently

A

according to joules law, a) heat generated in wires is proportional to the square of current so b) a low current is needed to reduce heat thus c) a high voltage is used

29
Q

list 4 sources of emf

A

dry cell, primary cell, secondary cell, mains

30
Q

what is a semi conductor

A

a MATERIAL with varying resistance

31
Q

what are two common semi conductors

A

silicon and gerarnium

32
Q

what is valence

A

amount electrons in an atoms outer shell needed to fill the shell

33
Q

what happens to a semi conductor like silicon when it heats up

A

a POSITIVE HOLE is left after an electron leaves

34
Q

what is intrinsic conduction

A

conductivity in a pure semicondunctor material due to factors like HEAT or LIGHT

35
Q

what is doping in semiconductors

A

adding impurities to increase extrinsic conductivity

36
Q

what is a p-n diode

A

when P TYPE and N TYPE semiconductor materials are joined to allow CURRENT to flow in ONE DIRECTION

37
Q

what is the depletion layer in a P-N DIODE

A

a neutral region where the electron holes and electons have filled each other and there no CHARGE CARRIERS

38
Q

what is required for a P-N DIODE to work

A

for voltage to exceed JUNCTION VOLTAGE that exists in DEPLETION LAYER AND to be connected in FORWARD BIAS

39
Q

what is forward bias

A

when the POSITIVE TERMINAL is connected to the p-type and the NEGATIVE TERMINAL is connected to n-type

40
Q

what happens if a semicondictor is connected in reverse bias

A

depletion layer widens, current doesnt flow except for current leakage, diode eventually breaks

41
Q

what unit is current measured in a) forward biased diode and b) reverse biased diode

A

a) milli amps and b) micro ampls

42
Q

example of material added to a) p-type dope silicone and b) n-type dope silicone

A

a) boron b) phosphorus

43
Q
A

physics (7 decks)

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