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P6 Flashcards

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1
Q

What is current?, and when will current flow through a circuit?

A
  • Current is the flow of electrons around a circuit.

- Current will only flow if there is a voltage across the component.

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2
Q

What is voltage?

A
  • Voltage is the driving force that pushes the current around the circuit.
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3
Q

What is current and voltage measured in?

A
  • Voltage = Volts

- Current = Amps

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4
Q

What is resistance?

A

Resistance is anything in the circuit that reduces the current.

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5
Q

What is resistance measured in?

A
  • Ohms
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6
Q

How is resistance caused in a circuit?

A

Resistance is caused when elections collide with atoms in the metal. These collisions cause the metal atoms to vibrate. The more atoms which vibrate the more the atoms get “in the way” of the electrons, meaning more collisions occur.

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7
Q

How does resistance effect temperature of a conductor?

A

The increased vibration of the atoms results in an increased temperature of the conductor.

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8
Q

What is another term for a Variable Resistor?

A

A “rheostat”.

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9
Q

How do variable resistors work?

A

They are a long coil of wire with a metal slider on the top. As you move the slider the length of the wire the current travels through changes.

Longer wires have more resistance, less current.
Shorter wires have less resistance, more current.

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10
Q

Give two uses of variable resistors?

A
  • Controlling the brightness of a light bulb.

- Controlling the speed of a motor.

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11
Q

What is the purpose of potential dividers?

A

To split the voltage in a circuit, this allows for different output voltages depending on resistance.

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12
Q

How are resistance and voltage related in a potential divider?

A

The larger the share of resistance a component has, the larger the share of the total voltage it also has.

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13
Q

Why are potential dividers useful?

A

They allow devices to be run which have a different operating voltage than the power supply.

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14
Q

What is the equation for voltage out?

A

V out = V in * (R 2 / (R1 + R 2))

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15
Q

What is the equation for resistance ?

A

Resistance = voltage ÷ current

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16
Q

What do voltage current (V-I) graphs show ?

A

Shows you how current varies as you change the voltage.

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17
Q

What is the current through a resistor proportional to ?

A

The voltage.

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18
Q

In series circuits how do you work total resistance ?

A

Sum of the individual resistances.

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19
Q

What has a lower resistance ? Two resistors in parallel or a circuit with 2 resistors by themselves ?

A

2 resistors in parallel.

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20
Q

What does an LDR (light dependant resistor) do ?

A

In bright light, the resistance falls.

In darkness, the resistance is highest.

This makes it a useful device for various electronic circuits. E.g automatic lights.

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21
Q

In basic terms what is a transistor?

A

Transistors are small Electronic Switches.

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22
Q

Why are transistors useful?

A
  • So that a small current can control the flow of a much larger current.
  • They are much smaller than mechanical switches so can be integrated into circuits, such as logic gates.
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23
Q

What are the three main parts of a transistor?, and what do they do?

A
  • Base - Switch that controls if current can flow through the transistor. If there is no current flowing in the base then current can not pass through the transistor.
  • Collector - Current flies into the transistor through the collector.
  • Emitter - Current flows out of the transistor through the emitter.
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24
Q

What is the equation for current in a transistor?

A

Current (emitter) = Current (base) + Current (collector).

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25
What is an LED?
- Light emitting diode. | - Just a diode which emits a coloured light.
26
How does current flow through LED's?
Like any other diode, LED's only let current flow through in one direction.
27
Why are LED's better than 'normal' light bulbs?
- Use less power. | - Last longer.
28
Why are LED's often connected in series with a resistor?
To prevent it from becoming damaged by a too large current flowing through it.
29
What is a relay?
A relay is a switch which connects two separate circuits together.
30
How are relays safe?
They isolate the large current circuit from a low powered circuit, so the human operator only comes into contact with the low current circuit.
31
How does a relay work?
1) When the switch in the low current circuit is closed it turns on an electromagnet. This attracts an iron contact to the rocker. 2) The rocker pivots and closes the contacts in the high current circuit allowing current to pass through the high current circuit. 3) When the low-current switch is opened, the electromagnet stops pulling and the rocker returns. Then high current circuit is broken again.
32
What does Thermistor (Temperature - Depandant resistor) do ?
In hot conditions, the resistance drops. In cool conditions, the resistance goes up. useful for temperature sensors.
33
What are the two states for a logic gate ?
ON or OFF.
34
What does a NOT gate do ?
switches the signal off from on - on to off.
35
What does an AND gate do ?
Needs two on inputs (1) to work.
36
What does an OR gate do ?
Only needs 1 input to work, will work with 2.
37
What does a NAND gate do ?
Switches the signal of the and gate.
38
What does the NOR gate do ?
Switches the output or the OR gate.
39
What are logic gates made up of ?
Transistors.
40
What happens when a current carrying wire is put between 2 metal poles.
The two magnetic fields affect each other resulting in force on the wire.
41
What angle does the wire have to be at to experience full force.
90 degree's
42
In a motor what causes the force to get stronger.
If current or magnetic field is made stronger.
43
What happens in a motor if you change the diection of the magnetic field or current ?
The direction of the force will change.
44
What is the definition of a "magnetic field"?
"A magnetic filed is a region where Magnetic Materials (like iron and steel) and also wires carrying current experience a Force acting on them.
45
What sort of magnetic field is formed around a straight, current carrying wire?
The magnetic field is circular with the wire in the Center.
46
What shape are the magnetic fields in a rectangular coil?
The circular magnetic fields on each side of the rectangular coil overlap in the middle of the coil. This creates a magnetic field in the centre which is stronger. If the coil has many turns the magnetic field from each loop reinforce each other even more.
47
What sort of magnetic field is found inside a current carrying solenoid?
Outside the solenoid it acts as a bad magnet, so each end acts as a north and South Pole. Circular magnetic fields also form around the Center of the solenoid.
48
What are 4 factors which effect the speed of a motor?
1) Current 2) Turns on the coil 3) Stronger magnetic field 4) A soft iron core in the coil.
49
How can the direction of the motor be reversed?
By swapping the polarity or the DC power supply.
50
What connects a motor to the item which is being rotated?
The Axel.
51
How do "practical motors" work?
They use curved magnets they form a hollow cylinder, the coil spins inside the cylinder. The curved magnets have a radial magnetic field. This increases the magnetic field strength around the coil, so the motor is more efficient.
52
What is Fleming's Left-hand rule.
Thumb = motion First finger = Field Second Finger = Current
53
What does moving a magnet through a coil of wire do ?
Induces a Voltage
54
What happens if you move the magnet backwards and forwards through the coil.
You produce a Voltage that keeps swapping direction (an AC current)
55
How do generators work ?
As you turn the magnet, the magnetic field through the coil changes. This change in the magnetic field induces a Voltage which causes a current to flow in the wire.
56
Name the 4 factors that effec the size of an induced voltage.
1. ) Strength of magnet 2. ) The AREA of the COIL 3. ) The number of TURNS on the coil 4. ) The SPEED of movement
57
What are the 3 parts of a transformer?
- Primary coil - Secondary coil - Laminated iron core
58
What are the three uses/types of transformers?
- Step up - Step down - Isolating transformers
59
How does a step up transformer work?
- primary coil has fewer coils on the primary coil than on the secondary coil. - increase the voltage
60
How does a step down transformer work?
The secondary coil has fewer turns than the primary coil. - The voltage is decreased
61
How do isolating transformers work?
- same number of turns on the primary and secondary coil. | - the voltage remains the same
62
What do AC generators use instead of a split-ring commutator.
Slip rings and brushes
63
What does faster revolutions in a motor produce ?
More peaks causing a higher voltage overall.
64
How do transformers work?
The primary coil produces a magnetic field, and because the current is alternating it means the field in the iron core is constantly changing. This rapidly changing field induces a current in the secondary coil.
65
What type of current do transformers work with?
AC (Alternating current)
66
Why do transformers not work with DC (direct current)?
The magnetic field would be a constant size, meaning there would be no induction in the secondary coil.
67
What is the equation associated with transformers?
Voltage * current = voltage * current | Power on primary coil = power on secondary coil
68
How do diodes effect current?
Diodes only allow current to flow in one direction.
69
How can you tell which way the current flows through a diode?
The diode symbol has a triangle on it, the direction of the triangle is the direction which the current will travel in.
70
What type of Material is silicon?
A semiconductor (meaning it can still conduct but not as well as a conductor)
71
What are diodes made out of?
Silicon
72
Describe how diodes work:
- There are two types of silicon joined together in a "p and n" junction. - the n side of the junction has had an impurity added to provide more electrons. - the p side has another impurity added so there are fewer free electrons. These missing electrons are called "holes". - when there's no voltage across the diode the electrons and holes combine to create a region free of elections which acts as an insulator.
73
What do capacitors do?
Capacitors store charge
74
How are capacitors charged?
By connecting it to a power source, such as a battery. A current flows around the circuit so charge gets stored.
75
How does time effect the flow of current in a capacitor?
The flow of current decreases as time increases
76
What do Dynamos do ?
They rotate the magnet instead of the coil to produce AC current.
77
In a power station how is power generated ?
Rotating an electromagnet through a coil of wire.
78
How can the size of the output voltage in a dynamo be changed ?
Adding more turns to the electromagnetic coil.
79
How can the size and frequency of the output from a dynamo be changed.
Rotating the electromagnetic coil faster.
80
What is the equation for the output voltage from a transformer ?
primary voltage ÷ secondary voltage = Number of turns on primary ÷ Number of turns on secondary.
81
What is the equation for power loss ?
Power Loss = Current(squared) × resistance
82
What is needed when power companies up the voltage to 400,000 V ?
Big pylons with huge insulators.
83
What Isolating Transformers do ?
Isolating Transformers have an equal number of turns in the primary and secondary voltages. It minimises the risk of getting electrocuted because no live parts touch the earth lead, So you can't complete a circuit.
84
Why can't power stations use a high current ?
Loss of energy through heat.
85
What is miniaturisation ?
The reduce in size of electrical components.
86
What are the benafits of miniaturisation.
Smaller devices use less raw materials. Mist customers like smaller devices. More portable devices available. More powerful device can be created with me features.
87
What are the drawbacks of miniaturisation ?
It can be complex to produce small devices, and more expensive. Smaller devices can be more expensive and easier to lose. Issues surrounding ethics as more people gain access to computers for example - hacking, piracy and access to personal data.

Physics (6 decks)

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