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physics > Seneca, Electric Circuits And Current > Flashcards

Seneca, Electric Circuits And Current Flashcards

1
Q

How can you detect current at a point in a circuit?

A

Current has the same value at any point in a single closed loop.

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2
Q

How to calculate the flow of charge ?

A

Flow of charge (coulumbs) = current (amperes) × time (seconds)

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3
Q

What is an electrical conductor and insulator.

A

Conductor = allows charge to pass through it.
Insulators do not

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4
Q

Give an example(s) of an electrical insulator

A

Plastic and glass

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5
Q

What defines a conductor ?

A

Conductors have charges that are free to move, e.g. electrons in a metal.

An electrical conductor has lots of charges that are free to move.In a metal, the charges that are free to move are electrons.The electric current through the metal is the flow of these free electrons.

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6
Q

Define potential difference

A

Potential difference is the difference in the amount of energy that charge carriers have between two points in a circuit. It can be described as the energy transferred by unit charge passed.

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7
Q

How can potential difference be measured ?

A

By using a voltmeter ( PD measured in volts ).

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8
Q

How can potential difference be measured ?

A

By using a voltmeter ( PD measured in volts ).

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9
Q

Where does a potential difference flow ?

A

The energy is transferred to the electrical components in a circuit when the charge carriers pass through them.

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10
Q

How to calculate potential difference ?

A

Voltage = energy ÷ charge

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11
Q

Potential difference In terms of energy used.

A

A potential difference of one Volt is equal to oneJouleof energy being used by oneCoulombof charge when it flows between two points in a circuit.

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12
Q

What is an ammeter / function?

A

An ammeter measures the flow of current that passes through it.Ammeters have to be connected in series (in the same loop of the circuit) with the electrical component whose current you are measuring

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13
Q

How must voltmeters be placed in a circuit ?

A

Voltmeters must always be connected in parallel (on a separate branch of the circuit) with the two points being measured.

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14
Q

What two factors is curreny affected by ?

A

The resistance: If the resistance is increased, the current will decrease

The potential difference: If the potential difference is increased the current will increase

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15
Q

What is resistance measured in ?

A

Resistance is measured in ohms, Ω

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16
Q

How to calculate resistance ?
What is ohms law ?

A

Resistance = potential difference ÷ current

Called ohms law.

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17
Q

What factors can affect resistance?

A

Increasing the length of a wire, increases the resistance of the wire.

Decreasing the cross-sectional area of the wire increases its resistance.

So short, wide wires have less resistance than long, narrow wires.

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18
Q

What is an ohmic conductor ?

A

A conductor that obeys ohms law

The current through an ohmic conductor (at a constant temperature) is directly proportional to the potential difference across the resistor.This means that the resistance remains constant as the current changes.

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19
Q

How to calculate the resistance of a wire ?

A

Resistance (in ohms) is proportional to (α) the length (in metres) divided by the cross-sectional area (in metres squared).

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20
Q

How to calculate wire thickness ?

A

The cross-sectional area (A) of a circular wire is equal to π times its radius (r) squared.

Therefore, doubling the thickness of a wire quadruples its cross-sectional area.

21
Q

How to plot a current voltage graph ?

A

We can plot a current-voltage graph by varying the potential difference across a circuit component

The current-voltage graph is a straight line obeying Ohm’s Law:
current = potential difference/resistance.The slope of the graph is equal to 1/resistance.

The constant slope (straight line graph) tells us that the resistance is constant.

22
Q

How to plot a graph for current / voltage in a fillament lamp

A

The gradient (slope) decreases at larger potential differences.

When the current through a filament (thin wire) lamp increases, the temperature of the lamp increases.

This increases the resistance of the lamp and causes the graph to curve.

23
Q

Where does the current from a supply go in a circuit?

A

Flow of current transfers energy from the supply to the components.

24
Q

Equation for power

A

power = current x potential difference
Measured in Watts (w)

The total energy transferred to a component is equal to the power multiplied by the time a current flows for.
Energy = power × time

25
Equation linking power, current and resistance.
power is equal to the current squared multiplied by the resistance.
26
What is the heating affect ?
Electric current does work to move through the resistor.Some of the kinetic energy of electrons moving through the resistor is transferred to heat energy. This is due to collisions between the electrons and the ions present in the resistor.We can reduce heat energy lost in a circuit by using low resistance wires.
27
Advantages of the heating affect
We can use electric current to generate useful heat.An example of this is a kettle to boil water .Lightbulbs use filaments with a high resistance. The filaments get very hot when a current flows through them which makes them emit light. Fuses get hot and melt when the current in a circuit becomes dangerously large. This is an important safety feature of circuits.
28
Disadvantages of the heating effect
Energy is wasted when electricity is transferred from a power plant to our homes because the transmission wires heat up. Some components work less efficiently when they get hot.
29
What is a diode ?
A diode is a component that only allows current to flow through it in one direction.
30
What is a rectifier ?
A rectifier is a component that turns an alternating current (repeatedly changes direction) into a direct current (one direction). Diodes act as rectifiers as they diode block the alternating current when it changes direction.
31
Use of a thermistor
A thermistor is a component thats resistance changes with its temperature. Usually, increasing temperature decreases the resistance. We can use a thermistor to turn a heater off when a house reaches certain temperatures.
32
Use of a light dependent resistor (LDR)
A light dependent resistor (LDR)s resistance changes with light intensity. Usually, increasing light intensity decreases the resistance. We can use LDRs to switch lights on when it gets dark or to know whether or not a camera phone needs to use “flash”.
33
What is the symbol for a motor ?
An 'M' in a box
34
Diode affect on resistance
A diode cannot alter resistance.
35
How to calculate resistance in a series circuit.
In a series circuit, total resistance = the added resistance of all resistors.
36
Voltage in a series circuit through components. (Compared).
The voltage across each component is different
37
What is total voltage in a circuit equal to ?
Total voltage of energy sources = total potential difference across all components. Moving charges disperse through the current to components arriving back at the source with no charge left.
38
What is true of a series circuit?
All components are attached in a row. The current is equal everywhere in the circuit. The voltage across each component is different. The sum of the voltages across each component is the total battery voltage.
39
What is true of parallel circuits?
In a parallel circuit, components are connected on separate branches of wires to the energy source. Circuit components in parallel look like they have their own extra mini-circuit. When the current flowing through point A, where the wires split, the current is split between the two branches. The current through the battery is larger than the current through each of the individual branches.
40
How to find current in a parallel circuit ?
In a parallel circuit the current through the energy source is equal to the sum of (adding up all of) the currents in the separate branches. Total current through energy source = current through R1 + current through R2. Current different in different places of a parallel circuit.
41
Resistance in a parallel circuit
The combined resistance of two resistors in parallel is less than the resistances of either of the two resistors by themselves. Like water draining through a bucket
42
Advantages of parallel circuits in the home
Lamps connected in parallel in the energy supply in the home : Each lamp may be switched on and off separately If one lamp breaks, current still flows through the others
43
Practical example for resistance (water bucket)
Resistors in parallel are like water draining out of a bucket with a hole. If a second hole is drilled into the bucket the water (like adding another resistor in parallel) will drain faster. It does not matter how narrow the second hole is (how high its resistance is), it is always faster for water to flow through two holes instead of one.
44
Christmas lights often contain many bulbs connected together. In what type of circuit is this likely to be?
A parallel circuit - if one breaks the others can still work / current can flow to them.
45
Rule of resistance in a parallel circuit
the total resistance of two resistors in parallel is always less than the resistance of the smallest individual resistor.
46
Ohms law on resistance series
The total potential difference of the power supply is shared between the components.Therefore by Ohm's law, the component with the larger share of potential difference must be the component with the larger resistance. Current same at all points of the circuit.
47
Ohms law on resistance paralell
The current is split between the branches.The potential difference across each parallel-connected component is the same.Therefore by Ohm's law, the current must be the same through two components of the same resistance connected in parallel.
48
Power dissipation in a thermistor
When the temperature is low, the resistance of the thermistor is very high. As power = potential difference x current, most of the power is dissipated through the thermistor.When the temperature is high, the resistance of the thermistor is low, and most of the power is dissipated through the bulb. This means the bulb glows brighter

physics (13 decks)

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