Electrical systems Flashcards
1
Q
What is electricity?
A
Electricity is the flow of electric charges.
2
Q
What is electric current?
A
It is the rate at which electric charges flow.
3
Q
What is an electric circuit?
A
It is a path that allows electric current to flow through it.
4
Q
What is a series circuit?
A
It is where the electrical components are joined one after another to form a simple loop.
5
Q
What is a series circuit?
A
- It is where the electrical components are joined one after another to form a simple loop.
- Electric current passes through a single path in a series circuit.
6
Q
What is a parallel circuit?
A
- It is where the electric currents are divided into branches.
- Electric components are connected in each branch.
- Electric current passes through all branches of a parallel circuit.
7
Q
What are the advantages of series circuits?
A
It is simple to build.
8
Q
What are the disadvantages of series circuits?
A
- When more loads are added, the total resistance in the circuit increases.
- When one load is damaged, it affects the functionality of the other loads.
- When one load is faulty, it causes a break in the circuit.
- Hence, the circuit becomes an open circuit and electricity cannot pass through it anymore.
9
Q
What are the advantages of parallel circuits?
A
- When more loops are added, the total resistance in the circuit decreases.
- When one load is damaged, it does not affect the functionality of the other loads.
- When one load becomes faulty, it causes a break in its own path only.
- The rest of the circuits remain as closed circuits.
- Hence, electricity flows through them continuously.
10
Q
What is the symbol and SI unit of electric current?
A
Symbol: I
SI unit: ampere (A)
11
Q
What is used to measure electric current flowing in a circuit?
A
Ammeter.
12
Q
what are the correct steps to connect an ammeter to a circuit?
A
- The ammeter must be connected in series with other electrical components.
- The negative terminal of the ammeter is connected to the negative terminal of the power source.
- The positive terminal of the ammeter is connected to the positive terminal of the power source.
13
Q
What is the conventional current?
A
It is where current flows from the positive terminal of a battery to the negative terminal.
14
Q
What is electron flow?
A
It is where the electrons flow from the negative to the positive terminal in an electrical source.
15
Q
Describe the readings in several ammeters in a series circuit.
A
It is the same at every point
(I = I1 = I2 = I3 =…)
16
Q
Describe the readings in several ammeters in a parallel circuit.
A
It is the sum of the total electrical current
(I = I1 + I2 + I3 +…)
17
Q
What is potential difference?
A
It is the electrical energy required to move a unit of electric charge across the two points of an electrical component.
18
Q
What is the symbol and SI unit of potential difference?
A
Symbol: V
SI unit: volt (V)
19
Q
What does one volt of potential difference mean?
A
It means that one joule of potential energy is needed to move one unit of charge.
20
Q
What is used to measure potential difference across two points?
A
Voltmeter.
21
Q
How must the voltmeter be connected to a circuit?
A
It must be connected in parallel across the electrical components.
22
Q
Describe the readings in several voltmeters in a series circuit.
A
It is the sum of all the voltage
(V = V1 + V2 + V3 +…)
23
Q
Describe the readings in several voltmeters in a parallel circuit.
A
It is the same in each loop
(V = V1 = V2 =V3 =…)
24
Q
What is resistance?
A
The resistance in a component is the ratio of the potential difference across it to the current flowing through it.
25
What is the symbol and SI unit of resistance?
Symbol: R
SI unit: ohm (Ω)
26
What is the relationship between resistance and electric current?
The higher the resistance in a component, the higher the potential difference needed to move the electric charge through the component.
27
What is a resistor?
It can be used to resist the flow of electric current in a circuit.
28
What are the factors affecting the resistance in a wire?
- Cross-sectional area
- Length
- Type of material
29
What if a circuit only contains fixed resistors?
The resistance of a circuit cannot be changed unless the resistors themselves are changed.
30
What are variable resistors?
A variable resistor of rheostat allows us to adjust the resistance in a circuit.
31
What do rheostats do?
It allows us to adjust the resistance in a circuit. It is used to adjust the sound and volume of radios and brightness in light bulbs.
32
How can rheostats control the brightness of a lamp, when it is off?
When the slider is on the left, the short resistance wire offers low resistance. The current flowing through the circuit is large. Hence, the bulb lights up brightly.
33
How can rheostats control the brightness of a lamp, when it is on?
When the slider is on its right, the long resistance wire sets up a higher resistance. The current flowing through the circuit is smaller. Hence, the light bulb dims.
34
Describe the readings in several resistors in a series circuit.
It is the sum of all the resistance (R = R1 + R2 + R3 +...)
35
What changes when more than one resistor is added in a parallel circuit?
It decreases the resistance in a circuit. The current flowing through the light builb increases. The light bulb is brighter.
35
Describe the readings in several resistors in a parallel circuit.
It is determined by a reciprocal relationship (1/R = 1/R1 + 1/R2 + 1/R3 +...)
36
What changes when more than one resistor is added in a series circuit?
It increases the resistance in a circuit. The current flowing through the light bulb decreases. The light bulb is dimmer.
37
What is electrolysis?
It is a chemical moethod to break down a compound into its respective elements.
38
What is electroplating?
it is the process of coating an object with a layer of metals.
39
Why is electroplating carried out?
- It is to prevent objects made of iron and steel from rusting
- To enhance the appearance of an object such as making it more shiny
39
What can be seen when an electric current flows near a compass?
The electric current in the wire produces a magnetic effect around the wire. This causes the needle to be deflected.
39
How can the magnetic effect of a wire be increased?
- It can be increased by making current flow in a coil of wire called a solenoid.
- If an iron rod is placed inside a solenoid, the iron rod becomes a magnet.
- When the current is switched off, the iron looses its magnetism.
- This set-up is known as an electromagnet.
40
How does the magnetic effect work on telephones?
- In telephones, a changing magnetic effect causes a thin sheet of metal, diaphragm, to vibrate.
- The diaphragm is made of metal that can be attracted to magnets.
- When it is attracted to the electromagnet, as the person on the other end of the line speaks, his voice causes the current in the circuit to change.
- This causes the diaphragm in the earpiece to vibrate, producing sound.
41
How does the heating effect work on an electric current in a light bulb?
- The current flows through the highly coiled filament.
- The current causes the filament to heat up. The filament glows and gives out light.
41
How does the heating effect work on an electric current in a kettle?
- The heating element, nichrome, is covered with a layer of electrical insulation.
- The insulated element is in turn placed in a looped tube made of a good heat conductor.
42
What is power?
- The power of a circuit component is the amount of electrical energy converted to other forms of energy per unit time by the component.
43
What is the SI unit of power?
Watt (W)
44
How are electrical fires prevented in kettles and electric irons?
- These appliances need large currents to produce heat.
- However, the wires do not heat up as the components in the circuits resists the flow of electric charge.
- This ensures that the current is not large.
45
How may electrical fires be caused by plugs and electrical circuits?
- Large currents can occur when electrical circuits are damaged, misused or do not work properly.
- For example, inserting too many plugs into the same power socket may draw a large current.
- The large current generates heat, which may melt the insulation and cause a fire.
46
How can electric shocks occur in a damaged kettle?
- The wire at high potential is disconnected from the heating coil and touches the metal casing.
- The electric potential of the casing increases to 240 V.
There is a large potential difference between the ground and the kettle.
- Hence, if a person touches the metal casing, a current flows through his body into the ground.
47
What should we do to prevent electrocution?
- Switch off and pull out the plug from the socket before cleaning fans, television sets, computers and toasters.
- Never use electrical gadgets in wet places, because water can conduct electricity through our body.
- Do not touch electrical appliances with wet hands.
Avoid getting water into the sockets of appliances.
- Do not use an appliance until you are sure its dry.
- If electrical wiring is old and the insulation is peeling off, the wires inside may be exposed.
- If a person touches the wires, current may flow through his or her body.
- Call an electrican to repair damaged appliances or electrical cables.
- Never insert any item into an electrical socket. Avoid doing this even if the plastic or wooden material of the item is a good insulator.
48
What are three safety features found in electrical circuits?
Earth wire, fuse, circuit breaker.
49
What are the three types of wires found in a household?
Earth, neutral, live
50
What is the feature of a neutral wire?
The neutral wire, blue, is at 0V.
51
What is the feature of an earth wire?
The earth wire, yellow or green, is at 0V. It is connected to the ground or earth.
52
what is the feature of a live wire?
The live wire, brown, is at a high voltage. In Singapore, it is at 240V.
52
What are circuit breakers?
- A circuit breaker can also cut off an electric current. However, unlike a fuse, it does not need to be replaced.
- Each circuit breaker is a switch-like lever connected to a different part of the household circuit.
52
What is the purpose of a fuse?
- The fuse makes use of the heating effect of an electric current to switch off a large current.
- A large current causes a short, thin wire in the fuse to heat up and melt.
- A circuit breaker can also cut off an electric current. However, unlike a fuse, it does not need to be replaced.
53
What is the purpose of the earth wire?
It provides a path of low electrical resistance. The large current flows directly from the live wire into the ground or earth.
54
How do circuit breakers work?
- The main switch turns on or shuts off all electricity in a household.
- When the current in one part of the circuit is too large, usually only the circuit breaker for that part turns off (trips).
- The other circuits in the household remains switched on.
- When a damaged appliance or the damaged part of the circuit is fixed, the circuit can be switched on again using the circuit breaker.
