P3 - Electricity

Question 1

What is static electricity?

Answer 1

Static electricity is caused by rubbing two insulators together

• when rubbing two insulators are rubbed together electrons are transferred from one insulator to the other causing one object to be negatively charged and one to be positively charged.
• static electrons doesn’t occur in conductors as electrons flow in and out of them so they stay neutral
• is enough charge builds up it can cause sparks

Question 2

What are the basics of the topic?

Answer 2

Protons (+)
Electron (-)
like charges repel and opposite charges attract

Question 3

What is induced charge?

Answer 3

1) When a charged object is brought near a neutral object it can induce a charge on it and attract to it.
2) if object is negatively charged repels the electrons in the in the neutral object.
3) The protons in the neutral object are at the surface of the object attracting to the negatively charged object.

Question 4

What are electric fields?

Answer 4

• They are always from positive to negative
• The close the field line the stronger the electric field (Radial field)
• When field is the same strength everywhere (uniform field)

SAME CHARGES
- when there are the same charges lines ‘push against’ each other and repel.
OPPOSITE CHARGES
- when there are opposite charges the field lines join up from positive charge to negative charge. Opposite attract.

Question 5

Uses of static electricity?

Answer 5

Spray painting: all the paint droplets are charged (eg negative) The paint droplets repel when sprayed allowing paint to spread out and additionally an object which is painted (such as a car) is the opposite charge so the paint attracts to the object.

Dust precipitator: When dust passes the negatively charged grid they become negatively charged. While dust is rising the positively charge plates attract these dust particles and dust stick to the plates. This allows little to no dust particles escaping form chimney into environment.

Question 6

What are the dangers of static electricity?

Answer 6

Sparks can cause fires or possibly an explosion in gas stations.

Question 7

Current + equation:

Answer 7

Current is the rate of flow of charge. (How many coulombs pass a point per second)

Current (A) = charge (C) / time (s)
I = Q / t

Question 8

Voltage + equation:

Answer 8

How much energy each coulombs has.

Voltage (V) = Energy (J) / Charge (C)
V= E / Q

Question 9

Resistance + equation:

Answer 9

How hard it is for electrons to flow in a circuit.

Resistance (ohms) = Voltage (V) / Current (A)

Question 10

Resistance in insulators and conductors:

Answer 10

Insulators = high resistance 
Conductors = low resistance

Question 11

Power + equation:

Answer 11

Power is the rate of flow of energy

Power (W) = Energy (J) / Time (s)

Question 12

2nd power equation:

Answer 12

Power (W) = Current (A) x Voltage (V)

Question 13

What is an ammeter and voltmeter?

Answer 13

Ammeter: Measures current in a circuit and needs to be places in series
Voltage: Measures voltage in a circuit and needs to be places in parallel to component you want to measure.

Question 14

Current, resistance and voltage in a series circuit:

Answer 14

Current: It is the same everywhere
Voltage: It is shared
Resistance: it adds up

Question 15

Current, resistance and voltage in a parallel circuit:

Answer 15

Current: It is split
Voltage: It is the same everywhere
Resistance : It is the inverse reciprocal added up ( 1/TR =1/R1 + 1/R2 + 1/R3)

Question 16

How is the resistance in long and short wires?

Answer 16

Long wires = high resistance , low current

Short wires = low resistance , high current

Question 17

I-V graphs for resistors:

Answer 17

It is a linear graph –> it is an Ohmic component

Gradient = 1/R (reciprocal)

Question 18

I-V graph for a filament light bulb:

Answer 18

S shape line: As the current increases the filament increases in temperature as more coulombs pass through wire there are more collisions, heating up wire. Metal cations in wire vibrate more. This makes it harder for electrons to flow which increases resistance.

Question 19

I-V graph for diode:

Answer 19

Diode only allows electrons to flow in one direction so diode I-V graph is an exponential graph and it increases rapidly in one direction due low resistance in that direction. The other direction has a high resistance so electrons can’t flow.

Question 20

What is a variable resistor?

Answer 20

It is a resistor that can change resistance

Question 21

How does the light dependant resistor work?

Answer 21

The more light the less resistance, more current.

The less light the more resistance, less resistance.

Question 22

How does a thermistor work?

Answer 22

A thermistor is a temperature dependant resistor.
The higher temperature, the less resistance, the more current. (Like. automatic fans)
The lower temperature, the more resistance, the less current.

Question 23

What is alternating current ?

Answer 23

A.C current is current that is constantly changing direction.