Topic 3: Electric Circuits Flashcards
(76 cards)
1
Q
Define:
electric current,I
A
The rate of fow of charge in a conductor.
In other words, the amount of charge per second fowing past a point.
2
Q
What is the formula and SI unit for current?
A
Current: I = ∆Q / ∆t
Where:
∆Q = change in charge (coulombs)
∆t = change in time (seconds)
The SI unit of charge is the ampere, A, and represents 1 C/s.
3
Q
There is 20 Coulombs of charge that passed through in 10 seconds. Calculate the current.
A
I= ΔQ / Δt
=20C / 10s
=2A
4
Q
Current is measured using an ____________, which must be connected in ________ and should have ____________ resistance.
A
Current is measured using an ammeter, which must be connected in series and should have negligible resistance.
5
Q
What causes current in metallic conductors?
A
The flow of free, delocalised electrons.
6
Q
State the difference between conventional current and actual current.
A
Conventional current flows from positive to negative while actual current is a flow of electrons from negative to positive.
7
Q
If electrons are moving along a wire from left to right, where is conventional current moving?
A
Conventional current is moving from right to left.
Conventional current always refers to the flow of positive charge, and will always be opposite to the flow of electrons.
8
Q
By what proportion will the current change if the amount of charge transferred doubles and the time halves?
A
The current will be 4× larger.
I₀ = Q / t
given new Q’ = 2Q
and new t’ = (½)t
then: I’ = Q’ / t’
= 2Q / (½)t = 4(Q / t)
= 4I₀
9
Q
What is the gradient on a charge-time graph?
A
Current ( I = ΔQ/Δt)
10
Q
How do you work out charge in a current-time graph ?
A
area under the graph (Q = It)
11
Q
What is charge?
A
Charge is a fundamental property of matter that is carried by elementary particles, such as electrons and protons.
12
Q
What unit measures charge, and what signs can be given to it?
A
The Coulomb, C, is the SI unit of charge and can have values that are positive (for current or protons) or negative (for electrons).
13
Q
What are the rules for attraction of charges?
A
Opposite charges (+,-) are attracted towards each other.
The force of attraction varies proportionally with magnitude of charges.
14
Q
What are the rules for repulsion of charges?
A
Like charges (+,+ or -,-) are repulsed away from each other.
The force of repulsion varies proportionally with magnitude of charges.
15
Q
What must be true of the total charge in a closed system?
A
Total charge in a closed system will stay constant. This is the law of conservation of charge.
16
Q
A
17
Q
Describe the total charge before and after in the following closed system: 5 protons and 4 electrons collide with sufficient energy to create 4 neutrons and 1 proton.
A
Charge remains constant at +1.
Charge initially is: +5 + (-4) = +1.
In a closed system charge must be conserved. The final charge confirms this: 4(0) + (+1) = +1.
18
Q
What is elementary charge?
A
The smallest possible charge, equal to the charge of a proton.
19
Q
What is the value of elementary charge?
A
1.60 x10⁻¹⁹C
20
Q
Define:
voltage
A
The work done per unit charge a charge carrier has to do to move through a component.
21
Q
What is the formula and SI unit of voltage?
A
V=WQ
Where ;
* V = the potential difference (V)
* W = is the work done (J)
* Q = is the charge that the work is being done on (C).
Voltage is in SI units of volts, V, and represents 1 J/C.
22
Q
Potential Difference is measured using a ____________, which must be connected in ____________ and should have ____________ resistance.
A
Potential Difference is measured using a voltmeter, which must be connected in parallel and should have infinite resistance.
23
Q
How does the work done by a charge carrier affect the circuit?
A
- It will power components
- It will generate heat through resistance.
24
Q
Define:
resistance
A
Resistance is a measure of how difficult it is to pass current through some object. Many factors affect resistance, including: cross-sectional area, length, and general resistivity.
Though all materials have some resistance at room temperature, super-cooled superconductors have a resistance of zero.
25
What is the formula for calculating the total resistance of an object, and what are the SI units of resistance?
R = ρ × L / A
Where:
ρ = resistivity of the material in Ωm
L = length of the object along current in m
A = cross sectional area in m²
Resistance is in SI units of Ohms, Ω, and represents 1 Js/C².
26
If a wire is uniform, how does the resistance relate to the length?
The resistance is proportional to its length.
27
By what factor has total resistance changed if the length of a resistor is doubled?
The total resistance will also double.
From: R₀ = ρ × L/A
new L' = 2L
R' = ρ × L'/A
= ρ × 2L/A = 2(ρ × L/A)=2R₀
28
By what factor has total resistance changed if the cross-sectional area of a resistor is doubled?
The total resistance will decrease by ½.
From: R₀ = ρ × L/A
new A' = 2A
R' = ρ × L/A'
= ρ × L/2A = (ρ × L/A)(½)=R₀/₂
29
By what factor has total resistance changed if the length of a resistor doubles and the cross sectional area also doubles?
The total resistance will remain constant.
From: R₀ = ρ × L/A
new L' = 2L
new A' = 2A
R' = ρ × L'/A'
= ρ × 2L/2A = ρ × L/A=R₀
30
By what factor has total resistance changed of a wire, if the length doubles and the radius also doubles?
The total resistance will decrease by ½.
From: R₀ = ρ × L/A
new L' = 2L
new A' = 4A (since area goes as the square of the radius)
R' = ρ × L'/A'
= ρ × 2L/4A = ρ × L/2A=R₀/₂
31
Define and give the SI units for:
**Resistivity**
**Resistivity, ρ,** is the measurement of how much a certain material resists the flow of current, and has SI units of **Ωm**.
32
Describe the relationship between temperature and resistivity.
As the **temperature** of a conductor increases, its resistivity increases as positive ions **vibrate more**. At low temperatures, this relationship is **linear**.
33
What does resistvity depend upon?
* The material a conductor is made of
* Its current physical conditions
34
____________ have low resistivities, while ____________ have incredibly high resistivities.
**Conductors** have low resistivities, while **insulators** have incredibly high resistivities.
35
Why is copper a better conductor than insulator?
The conductor contains more free electrons per cubic metre of material than the insulator.
36
Are ionic crystals conductors?
Ionic crystals are insulators. Once molten the liquid conducts. Positive and negative ions are the charge carriers. The same thing happens in an ionic solution.
37
Are gases conductors?
Gases are insulators but if you apply a high enough voltage electrons get ripped out of atoms, giving you ions along a path. You get a spark.
38
Explain what semiconductors do.
Semiconductors can release more charge carries when energy is supplied to them, decreasing their resistance.
39
How do semiconductors conduct without any energy supplied to them?
Semiconductors conduct better than insulators but not as well as standard conductors.
40
State the three semiconductors we look at and what they are sensitive to.
* Thermistors are sensitive to temperature
* LDRs and Diodes are sensitive to light
41
Why is silicon one of the best semi-conducting materials?
At a low temperature silicon is a poor conductor. As the temperature of the silicon rises, more electrons break free from the silicon atoms and so it becomes a better conductor.
42
What are semiconductors commonly used for?
For sensor circuits due to the resistance of a semiconductor relying on exterior conditions.
43
Why do semiconductors have a higher resistivity than metals?
There are fewer charge carriers available.
44
What is a superconductor?
A conductor whose resistance is zero.
45
What don't superconducting wires do?
Become hot and have no resistance because electrons can flow through them without any transfer of energy.
46
What must a material be to go superconducting?
Cooled below its transition (critical) temperature around, 10K (-263°C).
## Footnote
Scientistists are currently trying to develop superconductors that work at higher, more sustainable temperatures.
47
What the difference between a perfect and a real insulator?
A perfect insulator wouldn't have any charge carriers so n=0 in the formula and you'd get no current. Real insulators have a very small n.
48
What does this symbol stand for in a circuit diagram?
| Highlight the link and go to it cause I can't afford images :P
## Footnote
https://i.pinimg.com/564x/38/30/9e/38309e5bdb3098fd45ffae6f2831d9a8.jpg
This is a **cell**. Cells will always have a larger positive terminal (labeled +) and a smaller negative terminal (labeled –).
**Conventional current** always flows from + to – around the circuit.
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## Footnote
https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcSoQqZkz7SwpHnh3Icfnlm5FN8MnGxK2qXK6igN2FmnAxnK-ZM8NnARwfZTtwkhqN-Vjik&usqp=CAU
49
What does this symbol stand for in a circuit diagram?
| Highlight the link and go to it cause I can't afford images :P
## Footnote
https://www.iso.org/obp/graphics/grs/4d93d14e-708c-4937-aa30-b3c41d47c048_200.png
**Fixed Resistor**:
Restricts the flow of electrical current can be used to limit the flow of current to a particular component.
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## Footnote
https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcQ0BUFEV-NOkwtFNRfRUYweVvAje9pUkDVgiQ&s
50
What does this symbol stand for in a circuit diagram?
| Highlight the link and go to it cause I can't afford images :P
## Footnote
https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcRHJ41FsO3qm67mOGuyFYKAm1Bd5a7onD6UGQ&s
A **filament lamp** consists of coiled up wires that heat up as a current passes through them to emit light.
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## Footnote
https://www.shutterstock.com/image-vector/lamp-symbol-physics-electric-circuit-260nw-2352964077.jpg
51
What does this symbol stand for in a circuit diagram?
| Highlight the link and go to it cause I can't afford images :P
## Footnote
https://thumbs.dreamstime.com/b/caution-fuse-symbol-sign-white-background-223441788.jpg
**Fuse** - A safety device which melts to break the circuit if the electrical current flowing through it exceeds a specified value.
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## Footnote
https://d1e4pidl3fu268.cloudfront.net/8622a1f3-7756-4480-bf70-1bc7791f90d0/Fuse.crop_605x454_87,0.preview.jpg
52
What does this symbol stand for in a circuit diagram?
| Highlight the link and go to it cause I can't afford images :P
## Footnote
https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcRPv-n3b7Y3DEAqWTBrKihutB4Ln_UBFbLGlQ&s
**Voltmeter:** Instrument used to measure potential difference.
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## Footnote
https://www.shutterstock.com/image-vector/electronic-symbol-voltmeter-vector-illustration-260nw-2138872303.jpg
53
What does this symbol stand for in a circuit diagram?
| Highlight the link and go to it cause I can't afford images :P
## Footnote
https://www.clipartbest.com/cliparts/dc8/XEp/dc8XEpnzi.png
**Ammeter:** Instrument used to measure electric current.
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## Footnote
https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcQURDZb1Gx3Id05P3Y6cK2ZLl73Gf1zNSyJkA&s
54
What does this symbol stand for in a circuit diagram?
| Highlight the link and go to it cause I can't afford images :P
## Footnote
https://formatted-decks.s3.amazonaws.com/image/e6169004-a390-4e3a-b0be-27399b7802b7.jpg
**Light Dependent Resistor:** A semiconductor that only allows a current to flow in a single direction, called the forward bias.
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## Footnote
https://cdn.gcsesciencedictionary.co.uk/examples/images/7/detailed-47-Diode.JPG
55
Describe how the resistance of a LDR changes as light intensity increases.
As light intensity increases, the resistance of a LDR will decrease.
56
What does this symbol stand for in a circuit diagram?
| Highlight the link and go to it cause I can't afford images :P
## Footnote
https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcSZFuyKzjlhd5RSDWprvcd5z-q0aJdfBcwQRvt2gsqAEzt0yROAtK9nbzL9yyfHLeCyEf4&usqp=CAU
**Light Emitting Diode:** A diode that emits light as a current passes through it.
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## Footnote
https://www.slideegg.com/image/catalog/65242-led-circuit-symbol.png
57
What is the threshold voltage?
The potential difference below which the diode has infinite resistance.
58
What does this symbol stand for in a circuit diagram?
| Highlight the link and go to it cause I can't afford images :P
## Footnote
https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcQUnYC5-SuOQiFdGgTivY0ETXMX2-e6OS6FKn3OuoXYDkzn_RP-JbKbjyjHs5Z8eXZfwQ&usqp=CAU
**Negative Temperature Coeffiecient (NTC) Thermistor:** A semiconductor whose resistance will decrease with incresing temperature.
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## Footnote
https://images.wevolver.com/eyJidWNrZXQiOiJ3ZXZvbHZlci1wcm9qZWN0LWltYWdlcyIsImtleSI6ImZyb2FsYS8xNzM1NTY4NjI0MjU1LW50Y190aGVybWlzdG9yX3N5bWJvbC5qcGciLCJlZGl0cyI6eyJyZXNpemUiOnsid2lkdGgiOjk1MCwiZml0IjoiY292ZXIifX19
59
Explain why the resistance of a thermistor will decrease with an increase of temperature.
As temperature increases, conduction electrons are liberated, meaning there are more charge carriers and so current can flow more easily.
60
What does this symbol stand for in a circuit diagram?
| Highlight the link and go to it cause I can't afford images :P
## Footnote
https://th.bing.com/th/id/R.2e1b2123194b22125edc768466e7a2b3?rik=udno2yqKY8A7IQ&riu=http%3a%2f%2frimstar.org%2fscience_electronics_projects%2felectronic_symbols_for_schematics%2fthermistor_PTC_resistor_symbol.jpg&ehk=WybdplvziVTaDDu5jPTpWTHAX5jD16B6yfuMChWJxyQ%3d&risl=&pid=ImgRaw&r=0
**Positive Temperature Coeffiecient (NTC) Thermistor:** A semiconductor whose resistance will increase with incresing temperature.
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## Footnote
https://www.circuitstoday.com/wp-content/uploads/2017/10/PTC-Thermistor-Symbol.png
61
What does this symbol stand for in a circuit diagram?
| Highlight the link and go to it cause I can't afford images :P
## Footnote
https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcTGnxo_xSXLIko1P3yyta9sJupbaRiSruab6Q&s
This is a **capacitor**. Capacitors store charge and have units of farads.
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## Footnote
https://www.pcbtok.com/wp-content/uploads/2024/08/Mylar-Capacitor-Symbol.jpg
62
What does this symbol stand for in a circuit diagram?
| Highlight the link and go to it cause I can't afford images :P
## Footnote
https://makezine.com/wp-content/uploads/make-images/AtNnTsRDIUGCKxZD.jpg
This is a **switch**. Switches can be open (as shown in question) so that no current flows around the circuit, or closed so that both dots are connected and current flows.
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## Footnote
https://s3.eu-central-1.amazonaws.com/studysmarter-mediafiles/media/2667211/summary_images/image_hi3lw5r.png?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=AKIA4OLDUDE42UZHAIET%2F20250510%2Feu-central-1%2Fs3%2Faws4_request&X-Amz-Date=20250510T144729Z&X-Amz-Expires=604800&X-Amz-SignedHeaders=host&X-Amz-Signature=453a05c357cfe6b8b55f48dad8348d8c45462914dc17741c5fb34c52138a39ee
63
What does this symbol stand for in a circuit diagram?
| Highlight the link and go to it cause I can't afford images :P
## Footnote
https://tse3.mm.bing.net/th/id/OIP.AqqOR31Wyi5GavW5Z_z-_AAAAA?cb=iwc2&rs=1&pid=ImgDetMain
**Variable Resistor:**
Used to control current.
| Highlight the link and go to it cause I can't afford images :P
## Footnote
https://tse2.mm.bing.net/th/id/OIP.ZdNSzV0FAMbcgmxVNNSJwAHaHa?cb=iwc2&rs=1&pid=ImgDetMain
64
What is the formula for **Ohm's law**?
**Ohm's law** is written as:
I = V/R
or commonly: V = I×R
Where:
V = voltage in V
I = current in A
R = resistance in Ω
## Footnote
Ohm's Law V ∝ I
65
What must happen to the resistance, if the voltage is doubled in a circuit that has constant current flow?
The resistance must double also.
## Footnote
From Ohm's law: V=IR
Since current is held constant, voltage and resistance are directly proportional. Doubling voltage must result in resistance doubling.
66
What must have happened to the voltage supplied to a fixed resistance circuit, if the current suddenly drops to half original?
The voltage must have also dropped to half.
## Footnote
From Ohm's law: V=IR
Since R is held constant, V and I are directly proportional. Halving voltage means current must be halved also.
67
What must have happened to the resistance in a fixed voltage circuit, if the current suddenly doubles?
The resistance must have dropped to ½ original.
## Footnote
From Ohm's law: V=IR
Since V is held constant, R and I are inversely proportional. Doubling current means resistance must be halved.
68
Explain what is known as an ohmic conductor.
A conductor for which, under constant physics conditions, the curent through it is proportional to the poteintial difference across it. So the resistance is assumed to be constant.
69
What is the *I - V* characteristic for an ohmic conductor?
| Draw its graph
https://s3.eu-west-2.amazonaws.com/elements.cognitoedu.org/28f5cd63-e04a-4d6c-af10-150dee447d9a/resistor-iv-characteristic.png
| Highlight the link and go to it cause I can't afford images :P
70
What is the *I - V* characteristic for a
filament bulb?
| Draw its graph
https://s3.eu-west-2.amazonaws.com/elements.cognitoedu.org/5dd5b1bc-69b3-4009-a3f4-73f574cb4356/iv-graph-filament-lamp.png
| Highlight the link and go to it cause I can't afford images :P
71
Explain how the current in a filament bulb affects resistance and the shape of the *I - V* graph.
● The higher the current, the higher the
temperature of the metal filament.
● The higher the temperature, the higher the KE
of the metal ions and so the more they vibrate.
● This makes it harder for current to flow and so
the resistance of the bulb increases the curve on the *I - V* graph to become steeper.
72
What is the *I - V* characteristic for a diode?
| Draw its graph
https://mmerevise.co.uk/app/uploads/2022/11/Picture40-1-1024x824.png
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73
How does light instensity vary with resistance in LDRs?
| Draw its graph
https://s3.eu-central-1.wasabisys.com/evulpo-drive-mirror/en_UK/summary_assets/summary_asset_1662542688.png
| Highlight the link and go to it cause I can't afford images :P
74
How temperature vary with resistance in thermistors?
| Draw its graph
https://s3.eu-west-2.amazonaws.com/elements.cognitoedu.org/a8e6db69-a81b-41fb-9708-cb0d8cea20ea/thermistor-resistance-temperature-graph.png
| Highlight the link and go to it cause I can't afford images :P
75
What is the *I - V* characteristic for a thermistor?
| Draw its graph
https://www.passmyexams.co.uk/GCSE/physics/images/Graph_for_Thermistor.jpg
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76
