Topic 2 Electricity Flashcards
1
Q
What is current?
A
Flow of electrical charge
2
Q
What must a closed circuit have in order for current to flow?
A
Source of potential difference
3
Q
What 2 things does the current through a component depend on?
A
- Potential difference across it
- resistance of component
4
Q
How does a greater resistance across a component affect the current (for a given potential difference)?
A
Current is smaller
5
Q
What is the size of electrical current?
A
Rate of flow of charge
6
Q
What is the value of the current in a single closed loop?
A
same at any point
7
Q
What is potential difference?
A
Driving force that pushes charge round
8
Q
What is resistance?
A
Anything that slows flow down
9
Q
What does the resistance of an ohmic conductor do when the current changes?
A
Doesn’t change with the current (remains constant)
10
Q
What are 2 examples of ohmic conductors?
A
- Wire
- Resistor
11
Q
Through what component is the current (at a constant temperature) directly proportional to the potential difference across it?
A
Ohmic conductor
12
Q
What are 4 components where the resistance does change with the current through them?
A
- diode
- filament lamp
- thermistor
- LDR
13
Q
What does the resistance of a filament lamp increase with?
A
As temperature of filament increases
14
Q
What happens when the current through a filament lamp increases?
A
Filament lamp heats up more and so resistance increases
15
Q
What does the resistance depend on in a diode?
A
Direction of current
16
Q
Where does the current through a diode flow?
A
In one direction only
17
Q
When will a diode have a very high resistance?
A
If the flow of current is reversed
18
Q
What is the resistance of an LDR dependent on?
A
Light intensity
19
Q
What happens to the resistance of an LDR when light intensity increases?
A
Resistance decreases
20
Q
What happens to the resistance of an LDR when light intensity decreases?
A
Resistance increases
21
Q
What are 3 examples of applications of LDRs?
A
- automatic night lights
- outdoor lighting
- burglar detectors
22
Q
What is the resistance of a thermistor dependent on?
A
Temperature
23
Q
What happens to the resistance of a thermistor when the temperature increases?
A
Resistance decreases
24
Q
What happens to the resistance of a thermistor when the temperature decreases?
A
Resistance increases
25
What are **2 examples** of **applications** of **thermistors** as **temperature detectors**?
- **electronic thermostats**
- **car engine temperature sensors**
26
What happens if you **disconnect/remove one component** in a **series circuit**?
**Circuit is broken** and **all components stop**
27
What is the **rule** for **potential difference** in **series circuits**?
**Pd** is **shared** between the **components**
28
What is the **rule** for **current** in **series circuits**?
**Same current** through **each component**
29
What is the **size** of the **current** in a **series circuit determined by**?
**Total pd of cells** and **total resistance of circuit**
30
What is the **rule** for **resistance** in a **series circuit**?
**total resistance** of **two components** is the **sum** of **their resistances**
31
In **series circuits**, why is the **total resistance of two components**, the **sum of the resistance of each component**?
By **adding resistor in series**, **two resistors** have to **share total pd**
32
What are the **2 types** of **electricity supply**?
- **alternating current (ac)**
- **direct current (dc)**
33
What is **alternating current produced by**?
**Alternating voltages**
34
What is **alternating current**?
Current that **regularly changes direction**
35
What would **alternating current appear as** on a **voltage-time graph**?
**curve alternating** between **positive** and **negative voltages**
36
What **type of supply** is **mains electricity**?
**ac (alternating current)**
37
What **voltage** does the **UK mains supply (electricity in the home) have**?
**230V**
38
What is **direct current**?
**Current** that **flows** in **only one direction**
39
What is **direct current produced by**?
**Direct voltage**
40
What would **direct current appear as** on a **voltage-time graph**?
**straight horizontal line** at **constant voltage**
41
What **type of current** is **supplied by cells and batteries**?
**Direct current**
42
What is the **frequency** of the **UK mains supply (electricity in the home)**?
**50Hz**
43
What are **most electrical appliances connected to the mains supply by**?
**three core cables**
44
What does a **three-core cable contain**?
**three wires**, each with **copper core** and **coloured plastic coating**
45
How are the **wires** in a **three-core cable made easily identifiable**?
**Insulation** covering each wire is **colour coded**
46
What **colour** is the **live wire**?
**Brown**
47
What **colour** is the **neutral wire**?
**Blue**
48
What **colour** is the **earth wire**?
**Green and yellow stripes**
49
What are the **3 wires inside** a **three-core cable called**?
- **live** wire
- **neutral** wire
- **earth** wire
50
What does the **live wire do**?
**Carries alternating pd** from **mains supply**
51
What does the **neutral wire do**?
- **completes circuit**
- when **appliance operates normally**, **current flows** through **live** and **neutral wires**
52
What does the **earth wire do**?
- **safety wire**
- **stops appliance** from becoming **live**
53
What is the **voltage** of the **live wire**?
**230V (mains supply)**
54
What is the **voltage** of the **neutral wire**?
**Close to 0V**
55
What is the **voltage** of the **earth wire**?
**0V**
56
When is the **only time the earth wire carries a current**?
**If there’s a fault**
57
What **voltage** is the **body** and **earth** at?
**0V**
58
What **happens** if you **touch** a **live wire**?
**large pd produced across your body** and **current flows through you (large electric shock)**
59
What is **another way** of **saying a plug socket/light switch is turned off**?
**Switch** is **open**
60
Why is a **live wire still dangerous even when the switch is open**?
**Current isn’t flowing** but there’s still a **pd in live wire**
61
When you **make contact with a live wire, what is your body providing a link between**?
**Supply** and the **earth**
62
What does the **earth wire provide**?
**Low resistance path to earth** (instead of **passing through** a **person**)
63
What are **electrical appliances designed to do**?
**Transfer energy** to **components** in **circuit** when **current flows**
64
What **2 things** does the **amount of energy transferred by an appliance depend on**?
**How long appliance is switched on for** and **power of appliance**
65
When is **work done/energy transferred** in a **circuit**?
When **charge flows**
66
What is the **power** of an **appliance**?
**Energy it transfers per second**
67
What does a **kettle transfer energy from**?
**Mains ac supply**
68
What does a **kettle transfer energy to**?
**Thermal energy store** of **heating element inside kettle**
69
What does a **handheld fan transfer energy from**?
**Battery**
70
What does a **handheld fan transfer energy to**?
**Kinetic energy store of fans motor**
71
What are **appliances labelled with that is their maximum operating power**?
**Power rating**
72
What does the **power rating on an appliance tell you**?
**Maximum amount** of **energy transferred between stores per second** when **appliance is in use**
73
What does a **lower power rating on an appliance tell you**?
**Uses less electricity** in a **given time**- **cheaper** to run
74
What is the **National Grid**?
**System of cables** and **transformers linking power stations** to **consumers**
75
What does the **National Grid do**?
**Transfers electrical power** from **power stations** to **consumers**
76
What do **power stations often do** so that there’s **spare capacity to cope with high demand**?
**Run well below** their **maximum power output**
77
Why is the **national grid** an **efficient way** of **transferring energy**?
Uses **high pd** while keeping **current low** (**decreases energy lost** by **heating wires** and **surroundings**)
78
What are **used to increase the pd** from **power station to transmission cables** in the **national grid**?
**Step-up transformers**
79
What are **used to decrease the pd** (to a **much lower value**) for **domestic use** in the **national grid**?
**Step-down transformers**
80
How do **step-up transformers work**?
**Increases pd** which **decreases current**- **reducing power lost** due to **heating** in **cables**
81
What is **static electricity**?
When **certain insulating materials** are **rubbed together**, **electrons are transferred**, they become **electrically charged**
82
What happens when **certain insulating materials are rubbed together**?
**Negatively charged electrons** are **rubbed off one material** and **on to other**
83
What happens to the **material that gains electrons (static electricity)**?
Becomes **negatively charged**
84
What happens to the **material that loses electrons (static electricity)**?
Left with **equal positive charge**
85
What happens when **2 electrically charged objects are brought close together**?
**exert a force on each other**
86
What **type of force** is **electrostatic attraction or repulsion**?
**Non-contact**
87
What can **forces of attraction and repulsion cause objects to do**?
**Move**
88
What is a **method** to **see objects exert forces of attraction or repulsion on each other**?
- **suspend rod** (with **known charge**) from **piece of string** (**free to move**)
- **placing object** with **same charge** will **repel rod** (**move away** from **object**)
- **oppositely charged object** - **rod move towards object**
89
What happens when **electric charge builds on an object**?
**Pd between object and earth increases**
90
How are **sparks caused**?
When **pd between charged object** and **earth** gets **high enough**
91
What is an **electric field created around**?
Any **electrically charged object**
92
Where is an **electric field stronger**?
**Closer to charged object**
93
What happens to a **charged object** when **placed in the electric field** of **another object**?
**experiences a force**
94
What does a **high pd cause** between a **charged object** and an **earthed object**?
**Strong electric field**
95
How are **sparks produced**?
If **electric field** is **strong enough**, **charges** can be **forced though insulators (air)** and **spark will occur**
96
How do we **represent** an **electric field**?
Using **field lines**
97
In an **electric field diagram**, what do the **arrows** on **field lines show**?
What **force** would be **on positive charge**, if **placed in field**
98
When the **lines** are **closer together** on an **electric field diagram**, is the **field stronger** or **weaker**?
**Stronger**
99
When the **lines** are **further apart** and you get **further from charge** on an **electric field diagram**, is the **field stronger** or **weaker**?
**Weaker**
100
What happens if you **increase** the **distance between charged objects**?
**Strength of field decreases** and **force** between them gets **smaller**
101
What is the **force between charged objects caused by**?
**Electric fields interacting**
102
What will the **potential differences** around a **series circuit always add up to**?
**Total (source) pd**
103
How does **adding resistors** in **series affect** the **total resistance**?
**Increases**
104
In a **series circuit**, if a **component** has a **bigger resistance**, is its **share** of the **pd bigger** or **smaller**?
**Bigger**
105
Why does **adding a resistor** to a **series circuit increase** the **total resistance (3 points)**?
**Pd** across each **resistor** is **lower**
**Current** through each **resistor** is **lower**
**Total current reduced** as **current same everywhere**
106
What happens to the **cell pd** if **cells** are **connected** in **series**?
**Cell pd adds up, bigger pd**
107
What are **ammeters always connected in**?
**Series**
108
What happens if you **remove** a **component** from a **parallel circuit**?
**Hardly affect other components**
109
What is the **rule** for **pd** in **parallel circuits**?
**Same across all components**
110
What is the **rule** for **current** in **parallel circuits**?
**Total current = sum of currents** through **separate components (current shared between branches)**
111
In a **parallel circuit**, what does the **total current going into a junction** have to **equal**?
**Total current leaving**
112
What is the **rule** for **resistance** in **parallel circuits**?
If **2 resistors** in **parallel**, their **total resistance** is **less than resistance** of **smallest resistor**
113
What does **adding a resistor** in **parallel** do to the **total resistance**?
**Decreases**
114
Why does **adding a resistor** in **parallel reduce** the **total resistance (3 points)**?
**Current** has **more routes**- **easier to flow**
**Increases total current**
115
What can **dc series circuits** be **designed** and **used for**?
**Measure quantities** and **test components**
