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Physics > Electricity > Flashcards

Electricity Flashcards

1
Q

What are the different types of circuits?

A

Series, parallel, and mixed

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2
Q

What are the conditions for electric current to flow?

A

A source of potential difference between 2 points AND a complete circuit.

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3
Q

What does the battery do in the circuit?

A

Provides energy to push electrons through the circuit.

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4
Q

How is charge measured?

A

Coulombs (C)

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5
Q

What is the symbol for charge?

A

Q

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6
Q

What is the symbol for elementary charge?

A

e

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7
Q

What is AC?

A

Alternating current - the electrons often change direction.

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8
Q

What uses AC?

A

Fridges, fans

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9
Q

What is DC?

A

Direct current - electrons flow in only one direction.

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10
Q

What uses DC?

A

Laptops, cellphones, tvs (LEDs and transistors)

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11
Q

How is energy measured?

A

Joules (J)

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12
Q

What is potential difference?

A

The change in potential energy between each coulomb of charge.

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13
Q

What do resistors do?

A

Prevent damage from too much current.

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14
Q

What is tolerance in a resistor?

A

The allowable percentage error in the resistor.

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15
Q

What did Ohm discover?

A

In certain materials, voltage varies directly with current. (V=IR)

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16
Q

Where does Ohm’s law not apply?

A

In materials where the resistance varies with the temperature (lightbulbs).

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17
Q

What is current measured in?

A

Amperes (amps) (A)

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18
Q

What is the symbol for current?

A

I

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19
Q

What is the law of conservation of energy?

A

Energy lost at loads=energy gained at source

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20
Q

What is Kirchhoff’s Voltage Law in parallel?

A

V total=V1=V2= V3

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21
Q

What is Kirchhoff’s Voltage Law in series?

A

V total=V1+V2+V3

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22
Q

What is Kirchhoff’s Current Law in series?

A

I total=I1=I2=I3

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23
Q

What is Kirchhoff’s Current Law in parallel?

A

I total=I1+I2+I3

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24
Q

What is the resistance in series?

A

R total=R1+R2+R3

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25
Q

What is the resistance in parallel?

A

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

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26
Q

How is power calculated?

A

Work done, energy used, or moving charge.

27
Q

What is power?

A

The energy used per unit of time.

28
Q

How do you measure electrical energy (from a company)?

A

Kilowatt hours

29
Q

How is the cost of energy calculated?

A

Energy used x unit cost

30
Q

What is the Principle of electro Magnetism?

A

Whenever an electric current moves through a conductor, a magnetic field is created in the region around the conductor.

31
Q

What is the magnetic field of a straight conductor?

A
  • Circular around conductor
  • No poles
  • Reversing direction of current causes field lines to point in the opposite direction
32
Q

What is the right hand rule for a conductor?

A

x - pont right thumb into page
. - point thumb out of page
Curl fingers and which ever way fingers are pointing is the direction of the field lines

33
Q

What happens when a current-carrying conductor is formed into a coil or helix?

A

The magnetic fields add together and resembles the magnetic field of a bar magnet. It is more powerful.

34
Q

What is the right hand rule for a coil or helix?

A

Curl fingers in direction of current. Thumb points north.

35
Q

What is an electromagnet?

A

A device that exerts a magnetic force using electricity.

36
Q

What factors affect the strength of an electromagnet?

A
  • Current in helix
  • # of loops
  • Type of core
37
Q

Motor Principle

A

Current in a perpendicular external magnetic field will experience a force. The magnitude depends on the amount of current and the strength of the external magnetic field.

38
Q

What is the right hand rule for the motor principle?

A

Wrist at north, fingers at south, thumb in direction of current. Palm faces the direction of force, the way that the wire is pushed.

39
Q

What is the disadvantage of a single loop DC motor?

A

It is not very strong.

40
Q

How can the strength be increased in a single loop DC motor?

A
  • Increase the current [ :( ]
  • Increase the number of loops
  • Include a soft iron core
41
Q

What are the disadvantages of an armature DC motor?

A
  • Not continuous speed

- Won’t start if motor is turned off just as it reached split in split ring commutator because circuit is incomplete

42
Q

Why does an armature DC motor speed up and slow down?

A

Magnetic force is strongest when the coil is lined up with the external magnetic field so it weakens when it rotates away and the motor slows down.

43
Q

What did Faraday notice?

A

Current the secondary coil at the instant that the switch was opened or closed, when the magnetic field was changing.

44
Q

What did Faraday discover?

A

A changing magnetic field will induce an electric current in a conductor (there must be voltage).

45
Q

When an electric current is induced by a changing magnetic field, what direction does the current flow?

A

The induced magnetic current will always oppose the motion of the changing magnetic field.

46
Q

Right hand rule for Lenz’s Law

A

Push magnet towards core. Magnet is repelled so that end of the core is the same as the magnet. Point thumb north to determine direction of current.

47
Q

Lenz’s Law

A

For a current induced in a coil by a changing magnetic field, the electric current is in such a direction that its own magnetic field opposes the change that produced it.

48
Q

What does a generator do?

A

Converts mechanical energy into electrical energy.

49
Q

What are the main components of an armature DC motor?

A
  • Armature
  • Graphite brush
  • Split ring commutator
  • Field magnet
  • Coil
50
Q

What are the main components of an AC generator?

A
  • Field magnet
  • Armature
  • Split ring commutator
  • Coil
51
Q

What is the electromagnetic theory involved with an armature DC motor?

A

The motor principle

52
Q

What is the electromagnetic theory involved with as armature DC motor?

A

Faraday, Lenz’s Law

53
Q

How does an armature DC motor work?

A

(Current: B-A)

  • 2 N and S poles repel causing it to start rotating
  • N and S poles then attract after it rotates around
  • Rotates until it reaches split
  • No current at split but it keeps moving because of inertia
  • Insulator prevents N and S from attracting
  • New current goes A-B
  • Cycle continues
54
Q

How does an AC generator work?

A
  • Magnetic field is produced to oppose the motion, causing poles to change
  • New attraction opposes rotation
  • Poles stay the same and repel on other side, which opposes motion
  • Eventually becomes straight between 2 magnets and nothing happens but inertia keeps it moving
  • As it moves away it changes poles again, which opposes motion
55
Q

What are transformers for?

A

Change the current or potential difference to the amount needed.

56
Q

How does a transformer work?

A

1) Current induces a magnetic field in the primary coil.
2) Since current in primary coil is changing (AC), the magnetic field is also changing. This induces a current in the secondary coil.

57
Q

What does a step-up transformer do?

A

Increase potential difference.

58
Q

What does a step-down transformer do?

A

Decrease potential difference.

59
Q

What is the number of turns like in a step up transformer?

A

Primary

60
Q

What is the voltage like in a step up transformer?

A

Primary

61
Q

What is the current like in a step up transformer?

A

Primary > secondary

62
Q

What is the number of turns like in a step-down transformer?

A

Primary > secondary

63
Q

What is the voltage like in a step-down transformer?

A

Primary > secondary

64
Q

What is the current like in a step-down transformer?

A

Primary

Physics (4 decks)

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