Topic 3: Electric Circuits Flashcards
(124 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
Fill in the blanks:
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
How do you calculate the net charge on an object?
A
Q = ±ne
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
1.6 x10⁻¹⁹C
20
Q
what is the charge of an electron?
A
-e or -1.6 x10⁻¹⁹C
21
Q
what is the charge of an proton?
A
+e or +1.6 x10⁻¹⁹C
22
Q
What is number density?
A
Number of free electrons per cubic meter (m³) of material, higher means better electrical conductor.
23
Q
What are charge carriers?
A
Electrically charged particles, free to move in an object.
24
Q
How fast do charge carriers move?
A
slowly. free electrons repeatedly collide with metal ions as they drift, when switch on, they start moving all at once.
25
What is the formula and SI unit of current?
**I = nqvA**
Where;
* **n**= number of charge carries
* **q**= elementary charge
* **v** = mean drift velocity
* **A** = Cross-sectional Area
Current is in SI units of amperes or amps, A.
26
Why are metals good conductors? and what does that mean for the mean drift velocity?
Metals contain a large number of free electrons per unit volume, high value of n in I = nqvA meaning the mean drift velocity is small even for a high current.
27
How are current and wire cross-sectional linked?
Current is directly proportional to the cross-sectional area of a wire.
28
What happens if you half the radius of a wire?
The velocity of the electrons quadruple.
29
Define:
**voltage**
The work done per unit charge a charge carrier has to do to move through a component.
30
What is the formula and SI unit of voltage?
**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.
31
# Fill in the blanks:
Potential Difference is measured using a ____________, which must be connected in ____________ and should have ____________ resistance.
Potential Difference is measured using a **voltmeter**, which must be connected in **parallel** and should have **infinite** resistance.
32
How does the work done by a charge carrier affect the circuit?
* It will power components
* It will generate heat through resistance.
33
Define:
**resistance**
**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.
## Footnote
Though all materials have some resistance at room temperature, super-cooled superconductors have a resistance of zero.
34
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.
35
If a wire is uniform, how does the resistance relate to the length?
The resistance is proportional to its length.
36
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
37
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
38
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
39
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
40
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**.
41
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**.
42
What does resistvity depend upon?
* The material a conductor is made of
* Its current physical conditions
43
What is the structure of a metal?
Regular crystal structure OR lattice of positive ions, surrounded by delocalised electrons
44
# Fill in the blanks:
____________ have low resistivities, while ____________ have incredibly high resistivities.
**Conductors** have low resistivities, while **insulators** have incredibly high resistivities.
45
What is a conductor?
A material that allows the flow of electrical charge. Good conductors have a large amount of free charge carriers to carry a current.
46
Why is copper a better conductor than insulator?
The conductor contains more free electrons per cubic metre of material than the insulator.
47
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.
48
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.
49
What are semiconductors?
A material that has the ability to change its number of charge carriers, and so its ability to conduct electricity. Light dependent resistors and thermistors are both examples.
50
How can semiconductors affect resistance?
Semiconductors can release more charge carries when energy is supplied to them, decreasing their resistance.
51
How do semiconductors conduct without any energy supplied to them?
Semiconductors conduct better than insulators but not as well as standard conductors.
52
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
53
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.
54
What are semiconductors commonly used for?
For sensor circuits due to the resistance of a semiconductor relying on exterior conditions.
55
Why do semiconductors have a higher resistivity than metals?
There are fewer charge carriers available.
56
What is a superconductor?
A conductor whose resistance is zero.
57
What don't superconducting wires do?
Become hot and have no resistance because electrons can flow through them without any transfer of energy.
58
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.
59
what is an insulator and what gives insulators their properties?
they are poor conductors (conduct very little electricity) and this is because they have very few free electrons, in fact many insulators have values close to zero for n in I = nqvA.
60
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.
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://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
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://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
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://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
64
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
65
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
66
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
67
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.
| Highlight the link and go to it cause I can't afford images :P
## Footnote
https://cdn.gcsesciencedictionary.co.uk/examples/images/7/detailed-47-Diode.JPG
68
Describe how the resistance of a LDR changes as light intensity increases.
As light intensity increases, the resistance of a LDR will decrease.
69
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
70
What is the threshold voltage?
The potential difference below which the diode has infinite resistance.
71
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.
| Highlight the link and go to it cause I can't afford images :P
## Footnote
https://images.wevolver.com/eyJidWNrZXQiOiJ3ZXZvbHZlci1wcm9qZWN0LWltYWdlcyIsImtleSI6ImZyb2FsYS8xNzM1NTY4NjI0MjU1LW50Y190aGVybWlzdG9yX3N5bWJvbC5qcGciLCJlZGl0cyI6eyJyZXNpemUiOnsid2lkdGgiOjk1MCwiZml0IjoiY292ZXIifX19
72
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.
73
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
74
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
75
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.
| Highlight the link and go to it cause I can't afford images :P
## 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
76
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
77
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://cdn.savemyexams.com/uploads/2020/09/10.2.2-Potentiometer-symbol.png
**Potentiometer**: a single component which can act as a potential divider.
| Highlight the link and go to it cause I can't afford images :P
## Footnote
https://devxplained.eu/user/pages/02.blog/potentiometers/potentiometer.svg?decoding=auto&fetchpriority=auto&g-982d5237
78
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
79
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.
80
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.
81
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.
82
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.
83
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
84
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
85
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.
86
What is the *I - V* characteristic for a diode?
| Draw its graph
https://mmerevise.co.uk/app/uploads/2022/11/Picture40-1-1024x824.png
| Highlight the link and go to it cause I can't afford images :P
87
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
88
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
89
What is the *I - V* characteristic for a thermistor?
| Draw its graph
https://www.passmyexams.co.uk/GCSE/physics/images/Graph_for_Thermistor.jpg
| Highlight the link and go to it cause I can't afford images :P
90
What is **electromotive force (emf)**,*ε* ?
**Electromotive force** - The energy per unit charge a cell or pwer source transfers to charge carries.
91
# Fill in the blanks:
____________________ describes the energy given to charge carries while ________________ describes the energy taken from them.
**Electromotive force** describes the energy given to charge carries while **potential difference** describes the energy taken from them.
92
What is the unit of electromotive force (emf) ?
V
93
State the equation linking emf (ε), energy (E) and charge (Q).
E =εQ
Where;
ε = electromotive force in V
E = energy given to a charge carrier
Q = Charge of a charge carrier
94
Define:
**Internal Resistance**, *r*.
**Internal Resistance**, *r* - The small amount of resitiance found in almost all cells or power sources.
95
What is the symbol for internal resistance? What is the symbol for the load resistance?
Internal:
*r*
Load:
*R*
96
Define:
**Lost volts**, *v*.
**Lost volts**, *v* - the energy per unit charge lost to internal resistance, causing the cells to heat up.
97
What is *I × r* sometimes called?
Lost volts
98
Define:
**Terminal P.D**, *V*.
**Terminal P.D**, *V* - The effective emf of the cell once lost volts have been considered.
99
Derive the equation to calculate the emf of a supply from the current, load resistance and internal resistance?
ε= V + v
ε = V + Ir
ε= IR + Ir
ε = I (R + r)
## Footnote
ε = electromotive force (emf) in volts (V)
V = terminal P.D in volts (V)
v = lost volts in volts (V)
I = current in amperes or amps (A)
R = load resistance in ohms (Ω)
r = internal resistance in ohms (Ω)
100
How would I draw a cell with emf ε and internal resistance r on a circuit diagram?
https://cdn.savemyexams.com/uploads/2020/09/10.1.1.5-Internal-resistance-circuit.png
101
(core practical) What method and calculations would I use to find the internal resistance and emf of a cell?
Use a variable resistor and record V and I. Plot a pd-current graph. The emf is the y - intercept and the internal resistance is the negative of the gradient.
## Footnote
https://s3.eu-west-2.amazonaws.com/elements.cognitoedu.org/de265866-7364-438e-a1d4-7f9a6ae56481/emf-internal-resistance-graph.png
102
What is **Kirchoff’s First law**?
**Kirchoff’s First law** - The total current entering at a junction in a circiut must be equal the total current leaving that juction
103
What is Kirchoff’s First Law a consequence of?
the conservation of charge
104
What is **Kirchoff's Second Law**?
**Kirchoff's Second Law** - the sum of potential differences around a closed loop in a circuit must equal in a circuit must equal the total emf in that loop.
105
What is Kirchoff’s Second Law a consequence of?
the conservation of energy
106
how are ammeters connected in circuits and what is the resistance of them?
Connected in series, designed to be close to zero resistance.
107
how are voltmeters connected in circuits and what is the resistance of them?
Connected in parallel, designed to have close to infinite resistance so that none of the current flows through them.
108
what is the rule for current in series circuits?
stays the same
I = I₁ = I₂ = I₃ =...= Iₙ
109
what is the rule for current in parallel circuits?
splits at junctions
I = I₁ + I₂ + I₃ +...+ Iₙ
110
what is the rule for voltage in series circuits?
Splits, the voltage of the cell is equal to the sum of the voltages across the components (not necessarily and equal split).
V = V₁ + V₂ + V₃ +...+ Vₙ
111
what is the rule for voltage in parallel circuits?
The same, each branch has the same voltage as the cell (so would split if there were more than one component on the same branch).
V = V₁ = V₂ = V₃ =...= Vₙ
112
What is the equation for total resistance in a series circuit?
R(total) = R₁ + R₂ + R₃ +...+ Rₙ
| opposite to spring constant and capacitors
## Footnote
This is because all the resitors will have the **same current** flowing through them but their **potential difference's** sum.
113
How do you find the total resistance in a parallel circuit?
¹/R(total) = ¹/R₁ +¹/R₂ + ¹/R₃ +...+ ¹/Rₙ
R(total) = (¹/R₁ + ¹/R₂ + ¹/R₃ +...+ ¹/Rₙ)-¹
| opposite to spring constant and capacitors
## Footnote
This is because all the resitors will have the **potential difference** flowing through them but their **same current's** sum.
114
What is a potential divider?
A circuit consisting of two ( or more) resistors and fixed emf source, which can deliver a reduced output potential difference to a circuit connected in parallel to one of the resistors.
115
State the three main purposes of potential dividers.
To provide a variable potential difference.
To enable a specific potential difference to be chosen.
To split the potential difference of a power source between two or more components.
116
What is the equation for the potential divider ratio?
V₁/V₂ = R₁/R₂
117
What is the equation for the potential divider output?
Vₒᵤₜ =Vᵢₙ (R₂/R₁+R₂)
118
what is a potentiometer and what does it consist of?
a single component which can act as a potential divider.
It consists of a coil of wire with a sliding contact
A variable output voltage can be varied by moving a slider along the component
119
# Fill in the blanks
A ____________ is used to control the current in a circuit while a ________________ is used to control potential difference in a circuit.
A **rheostat** is used to control the current in a circuit while a **potentiometer** is used to control potential difference in a circuit.
120
How would the potential difference over R₂ change as
the light intensity increases in the following circuit?
## Footnote
https://www.petervis.com/electronics%20guides/calculators/LDR/voltage-divider-circuit-for-ldr-config-1.gif
As light intensity increases, the resistance over the LDR will decrease. This means that the fixed resistance R₂ will take a larger ratio of the circuit potential and the potential difference across it will increase.
121
Define;
**Power**, *P*.
The power of a component describes the rate at which energy is transferred to it or the rate at which energy is lost to resistance.
122
State the component power equations
P = IV
P = I²R
P = V²/R
123
The total ________________________ to a component is dependent on the time that a current flow through it.
The total **energy transferred** to a component is dependent on the time that a current flow through it.
124
How can you calculate the work done over a given time period, by a component with a known potential
difference and current?
E = Pt
E = IVt
E = I²Rt
E = V²t/r
