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XPHB 5th Form Physics THT > 07 Energy and Voltage- 4th Form COPY > Flashcards

07 Energy and Voltage- 4th Form COPY Flashcards

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1
Q

Why would an appliance NOT need an Earth wire?

A

It is double insulated

It has a plastic casing OR the electrical components are incased by plastic

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2
Q

Why are the bulbs dimmer in the second circuit?

A

Voltage is shared between bulbs in series

Less voltage across each bulb therefore bulb is dimmer.

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3
Q

Define voltage

A

Energy per unit charge either supplied by a cell, or transferred to a component.

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4
Q

What component symbol is shown below?

A

Light dependent resistor

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5
Q

What type of current is shown in the image?

A

Alternating current

Current that constantly changes direction

i.e. 50 Hz or 50 times a second

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6
Q

What is voltage measured in?

A

Volts or V

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7
Q

What is the voltage across a cell or power supply a measure of?

A

The energy transferred from chemical store electrically to the wires per coulomb

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8
Q

What component symbol is shown below?

A

bulb

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9
Q

What component symbol is shown below?

A

ammeter

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10
Q

Define current

A
  • The rate of flow of charge

OR

  • the number of coulombs passing a point in a circuit per unit time

(It is not the speed of the electrons!)

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11
Q

Which wire is circled in the image?

A

Earth wire

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12
Q

What happens to the total resistance and current in a circuit as more bulbs are added in parallel

A

Adding bulbs in parallel decreases the total resistance

V=IR

I = V / R

as resistance decreases, current increases for the same voltage

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13
Q

The IV graph below shows a line for fixed resistor. How would the line change for a resistor with half the resistance?

A

It would be steeper

It would have double the gradient

It would have double the current for the same volts

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14
Q

What is the effect of current in a resistive wire?

A

Moving electrons in the wire collide with the metal ions

They transfer energy electrically to the wire

The wire heats up -gains a thermal store

When hot enough the wire may glow - radiate energy

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15
Q

How will the current change if the resistance of a circuit is decreased for the same voltage?

A

current will increase

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16
Q

How does a fuse work?

A
  • If the current exceed the fuse rating (surge in current)
  • the fuse wire heats up and melts
  • This breaks the circuit and isolate the appliance
  • protecting it from overheating/fire
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17
Q

To investigate how the currect varies with voltage in a filament bulb, fixed resistor and diode you should use the cirucit below.

Why does the circuit need a variable resistor?

A

To vary the voltage across the component

Independent variable is voltage

Dependent variable is current

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18
Q

The plastic around wires keep us safe. Explain

A

Plastic is an insulator.

No current can flow through an insulator

no risk of electric shock

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19
Q

What is resistance?

A
  • The tendency of a material to resist the flow of an electrical current.
  • A measure of how much voltage is needed per amp of current.
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20
Q

How does the resistance vary with light intensity on a LDR?

A

As light intensity increases, resistance decreases

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21
Q

Below is an IV graph for a…..

A

diode

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22
Q

How is voltage related to energy and charge?

A

V=E/Q

Voltage = Energy / Coulomb

Voltage lost across a component is a measure of the energy lost across the component per coulomb

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23
Q

What is power measure in?

A

Watts (W)

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24
Q

How does an Earth wire and a fuse work together to protect the user of an appliance

A
  • The Earth wire is connected to the metal casing of the appliance
  • if the live wire works loose (fault) and touches the metal casing
  • there is a surge in current through to the Earth wire
  • this melts the fuse wire
  • isolating the appliance
  • preventing an electric shock
25
Q

What is a watt?

A

1 W = 1 J/s

I Watt = 1 joule per second

26
Q

What is a volt?

A

1 V = 1 J/C

1 volt = 1 joule per coulomb

27
Q

How does voltage related to current and resistance?

A

V=IR

28
Q

What is true about the current in a series circuit?

A

Current is the same everywhere in a series circuit

29
Q

What type of circuit is this? Series or parallel?

A

Series circuit

Only one path or branch in the circuit

30
Q

What are the prongs of a plug made of brass but the wires made of copper?

A

Brass is strong and will not bend

Copper is a good conductor of electricity and ductile (can be drawn into wires)

31
Q

What component symbol is shown below?

A

thermistor

32
Q

Below is the symbol for…

A

a double insulated appliance

33
Q

What is the Earth wire connected to in the appliance

A

The metal casing

34
Q

How does voltage across bulbs in a series and parallel circuit differ?

A

Current is conserved in all circuits

Series - current is the same everywhere in the circuit

Parallel - current splits between the branches- current into a junction equals current out of a junction

35
Q

What is the unit for current?

A

ampere / amps or A

36
Q

What component symbol is shown below?

A

buzzer

37
Q

What component symbol is shown below?

A

voltmeter

38
Q

What is the unit for energy?

A

joules (J)

39
Q

How is power related to current and voltage?

A

P=IV

40
Q

What component symbol is shown below?

A

Fuse

41
Q

What component symbol is shown below?

A

Light emitting diode

42
Q

How is energy related to current, voltage and time?

A

E = IVt

43
Q

A fuse protects the appliance and the user….explain

A
  • the fuse will blow if there is a surge in current to the appliance. This protects the appliance from overheating (being damaged)
  • the fuse will blow if a fault occurs in the appliance. The surge of current down the Earth wire blows the fuse and prevents an electric shock
44
Q

What component symbol is shown below?

A

motor

45
Q

Name the parts of a plug

A
  1. Cable grip

2 Neutral wire

  1. Earth wire
  2. Live wire
  3. Fuse
46
Q

Bulbs in series provide a larger resistance than bulbs in parallel

With this in mind, which circuit draws a larger current from the cell?

A

V = IR

I = V / R

as resistance decreases, the current increases for the same voltage

The second circuit draws a larger current from the cell, bulbs are in parallel and the total resistance is smaller than the first circuit (series circuit)

47
Q

What is the difference between d.c. and a.c. current/voltage

A

Direct current - current flows in one direction only (i.e. cell)

Alternating current - current continuously changes direction (i.e. mains supply)

48
Q

Each cell provides 3 V. In which circuit (series or parallel are the bulbs brighter?

A

Bulbs in parallel are brighter = both have 3V across them (brighter)

Bulbs in series have 1.5 v across each (dimmer)

Series- voltage is shared - VCell = V1 + V2

Parallel - each bulb gets the full voltage of the cell - Vcell = V1 = V2

49
Q

How does current differ between series and parallel circuits?

A

Current is conserved in all circuits

Series - current is the same everywhere in the circuit

Parallel - current splits between the branches- current into a junction equals current out of a junction

50
Q

How does the resistance of an LDR vary with light intensity?

A

As light intensity increases, resistance decreases

51
Q

Describe what it means when 1 A is passing through a circuit

A

1 A = 1 Coulomb per second

52
Q

The IV graph below is for an ohmic conductor…

Give an example of an ohmic conductor.

A
  1. fixed resistor
  2. wire (if at constant temperature)
53
Q

Below is the IV graph for a….

A

filament bulb

54
Q

Explain why the second circuit draws a lower current from the cell?

A

circuit with two bulbs in series - has larger resistance

V=IR

I = V/R

as resistance increases, current decreases for same voltage

55
Q

What component symbol is shown below?

A

diode

56
Q

For a wire - as temperature increases, resistance also increases.

The graph below shows the opposite.

What component is this graph for?

A

Thermistor

57
Q

What component symbol is shown below?

A

variable resistor

58
Q

What component symbols are shown below?

A

battery/two cells

&

solar cell

59
Q

What would happen if a plug is wired incorrectly and the live wire is attached to the Earth prong

A

The Earth prong is wired to the metal casing of the appliance

The metal casing of the appliance will be live with 240V wired to it.

Risk of electric shock to user

XPHB 5th Form Physics THT (20 decks)

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