Chapters 8-9 R#1 Flashcards
1
Q
Chapter 8: Electricity
A
2
Q
What are the two types of electric charges?
A
Positive charge (+) and Negative charge (–)
3
Q
What is the law of attraction and repulsion for charges?
A
Like charges repel, unlike charges attract.
4
Q
How can an object be classified based on its charge?
A
- Positively charged: more (+) than (–)
- Negatively charged: more (–) than (+)
- Neutral: equal number of (+) and (–)
5
Q
What are good conductors and why?
A
Metals, because they contain a large number of freely moving electrons allowing charge to pass.
6
Q
How do electricity or charges move through substances?
A
By the movement of electrons
7
Q
Explain how electrons transfer thermal energy through a metal can.
A
When the metal can is heated, the metal atoms/ions start to vibrate. These vibrating atoms/ions hit free moving electrons and propel them through the metal towards the colder part of the can.
(3 mark question, 4 point answer)
8
Q
What are insulators and why?
A
Rubber, wood, plastic, because they contain few freely moving electrons and don’t allow charge to pass.
9
Q
How can an insulator be charged?
A
By rubbing, transferring electrons between the objects.
10
Q
Why must the cloth be dry when charging an insulator by rubbing?
A
Water is a conductor and would prevent effective charge transfer.
11
Q
How can a conductor be charged by induction?
A
By bringing a charged rod close, allowing electrons to move, then grounding and removing the charge source.
12
Q
What is an electric field?
A
The region surrounding a charge where an electric force is exerted.
13
Q
What do electric field lines represent?
A
The direction and strength of the electric field; they originate from positive charges and enter negative charges.
14
Q
What does a battery do in a circuit?
A
Converts chemical energy into electrical energy.
15
Q
What is the voltage of a single cell?
A
1.5V
16
Q
What is the function of a bulb in a circuit?
A
Acts as an indicator for electric current.
17
Q
What is the function of a switch?
A
Controls the flow of current, typically drawn in an open position.
18
Q
What is an ammeter used for, and how is it connected?
A
Measures current (A) and must be connected in series.
19
Q
How is electric current defined and calculated?
A
The amount of charge passing per second:
𝐼 = 𝑄 / 𝑡
20
Q
What is conventional current direction?
A
From the positive terminal of the battery to the negative terminal.
21
Q
What is the direction of the flow of electrons and why?
A
Electrons flow from the negative terminal to the positive terminal as they are repelled by the negative charge of the negative terminal AND they flow against the flow of current.
22
Q
What is the function of a voltmeter and how is it connected?
A
Measures voltage (V) and must be connected in parallel.
23
Q
What is Ohm’s Law?
A
V = IR
24
Q
How is resistance calculated?
A
R = V / I
25
What happens to total resistance in a series circuit?
It increases:
𝑅(𝑇) = 𝑅(1) + 𝑅(2) + 𝑅(3)
26
What are disadvantages of series circuits?
If one component fails, all fail; brightness of bulbs decreases.
27
How is total resistance calculated in a parallel circuit? (for two resistors)
𝑅(𝑇) = (𝑅[1] x 𝑅[2]) / (𝑅[1] + 𝑅[2])
**multiply / add**
28
What are advantages of parallel circuits?
If one component fails, others work; bulbs maintain same brightness.
29
How do current and voltage behave in series vs parallel circuits?
In series: current same, voltage splits. In parallel: voltage same, current splits.
30
How does wire length affect resistance?
Longer wires have higher resistance.
31
How does cross-sectional area affect resistance?
Greater area results in lower resistance.
32
How does temperature affect resistance in metals?
As temperature increases, metal atoms gain kinetic energy and vibrate more, due to the increased collisions between the freely moving electrons and the vibrating lattice, resistance increases
33
How does temperature affect resistance in semiconductors?
Higher temperature decreases resistance.
34
What is the formula for resistance of a wire?
R = (ρxL) / A
35
What analogy explains current, voltage, and resistance?
* Current: Delivery crew carrying sandwiches
* Voltage: Energy sandwiches from battery to components
* Resistance: Traffic affecting crew’s movement
36
What is a rheostat?
A variable resistor used to control current.
37
What is a thermistor and how does it work?
A temperature-dependent resistor; lower resistance at high temperatures.
38
What is an LDR (Light-Dependent Resistor)?
A resistor that decreases in resistance when exposed to light.
39
What is a diode and how does it function?
A semiconductor that allows current to pass in one direction.
40
What happens when a diode is forward-biased? (connected forward)
It has low resistance and allows current to pass.
41
What happens when a diode is reverse-biased? (connected in reverse)
It has high resistance and blocks current.
42
What is an LED (Light Emitting Diode)?
A diode that emits light when forward-biased.
43
What are the three wires in a European plug?
* Live wire (carries electricity) **[Blue]**
* Neutral wire (closes circuit) **[Brown]**
* Earth wire (prevents shocks) **[Yellow/Green]**
44
What is a circuit breaker and how does it work?
A safety device that shuts down power when excessive current generates a strong magnetic field.
45
How does a fuse protect a circuit?
When high current passes through circuit (greater than normal current) they melt breaking the circuit and protecting any connected components
46
What are fuse ratings?
The fuse must be slightly larger than the normal operating current.
47
What is double insulation?
The outer case of a device is made of an insulator to prevent electric shocks.
48
What are earth wires and how do they work?
They provide low resistance path for electrons to flow through to the ground preventing electric shock in case the metal case becomes live or the insulation fails
49
What is a potential divider?
A circuit that divides voltage based on resistor values **connected in series**.
50
What happens in a variable resistor with a sliding contact?
Moving the slider changes the length, resistance, and voltage.
51
What is the difference between direct and alternating current?
* DC (Direct Current): Flows in one direction (batteries).
* AC (Alternating Current): Changes direction periodically (generators).
52
How do you charge a conductor negatively by induction?
To charge negatively by induction, bring a positively charged rod near a neutral conductor so that electrons in the conductor are attracted toward the rod. While the rod is in place, connect the conductor to ground; electrons will flow from the ground into the conductor, giving it a net negative charge. Then remove the ground connection and finally remove the rod.
53
Why does the V–I graph of a filament lamp deviate from a straight line?
* As current flows through a filament, it heats up, causing its temperature to increase.
* As temperature increases lattice of material vibrates more and collides more with electrons, therefore current decreases and resistance increases.
* This rising resistance results in a non-linear (curved or plateauing) V–I graph rather than a straight line as predicted by Ohm’s law for constant resistance.
54
What factors determine the resistance of a wire, and what is the governing formula?
The resistance of a wire depends on its material’s resistivity (ρ), its length (l), and its cross-sectional area (A). The formula is:
* 𝑅 = (𝜌 × 𝑙) / 𝐴
55
How do electric field lines indicate both the direction and strength of an electric field?
Electric field lines start from positive charges and end on negative charges. Their direction shows the field’s direction, and the closer the lines are to each other, the stronger the field at that region.
56
How does a potential divider work in a series circuit?
In a potential divider, the voltage drop across each resistor is proportional to its resistance. By adjusting the resistor values (or moving a slider on a resistance wire), you obtain a desired fraction of the total voltage.
57
What are the proper ways to connect an ammeter and a voltmeter in a circuit?
An ammeter is connected in series to measure the current flowing through the circuit, whereas a voltmeter is connected in parallel across a component to measure the voltage drop.
58
How does a diode function in forward and reverse bias?
* In forward bias, a diode has low resistance and allows current to pass
* In reverse bias, it exhibits high resistance and blocks current flow.
* This property is used, for example, in converting AC to DC.
59
What is the formula for electrical power in a circuit?
Power = Current x Voltage (P = IV)
60
How do you calculate energy transferred in an electrical circuit?
Use the formula: Energy = Current x Voltage x Time (E = IVt)
61
Why is earthing used in electrical appliances?
It provides a safe path with low resistance for current in case insulation fails and live wire touches metal casing causing it to become live, preventing electric shock.
62
Chapter 9: Magnetism
63
What is electromagnetic induction?
It is the process of generating voltage by moving a conductor through a magnetic field.
64
What factors affect the size and direction of induced voltage?
Speed of motion, strength of magnetic field, and direction of movement.
65
What is the structure and function of a transformer?
A transformer consists of two coils and changes the voltage of AC.
66
What is the transformer equation?
Vp/Vs = Np/Ns (Primary voltage / Secondary voltage = Number of turns in primary / secondary)
67
Why do transformers only work with AC?
Because a changing magnetic field is needed to induce voltage in the secondary coil.
68
What is the motor effect?
A current-carrying wire in a magnetic field experiences a force.
69
How does Fleming's left-hand rule work?
Thumb = motion, First finger = field, Second finger = current.
70
What is the basic structure of a simple electric motor?
Coil in magnetic field rotates due to motor effect.
71
How are electromagnets used in devices?
In relays, circuit breakers, and electric bells to control switching or movement.
72
What is the magnetic field pattern of a solenoid?
It resembles the field of a bar magnet: strong and uniform inside the coil.
73
What is the law of attraction/repulsion for magnets?
Like poles repel; unlike poles attract.
74
What are the basic properties of a magnet?
Magnets have a north and a south pole (there are no monopole magnets), are made of iron or steel, and do not affect non-magnetic materials.
75
What are permanent (hard) magnets and what are they made of?
Permanent magnets are made of steel and keep their magnetism for a long time.
76
What are temporary (soft) magnets and what are they made of?
Temporary magnets are made of iron and lose their magnetism after a short time.
77
How can steel be magnetized by stroking?
By moving a magnet on a steel bar in one direction many times.
78
How can steel be magnetized using DC current?
By moving a steel bar inside a coil that is carrying a DC current.
79
What are the methods to demagnetize a magnet?
* By hammering repeatedly from East to West
* By heating until red hot
* By moving a magnet inside a coil carrying AC, then reducing current to zero
80
What is a magnetic field?
It is the region surrounding a magnet where magnetic force acts.
81
How do magnetic field lines run around a magnet?
They come out of the north pole in all directions and go into the south pole from all directions.
82
How does the spacing of magnetic field lines relate to the field’s strength?
As the spacing between lines increases, the magnetic field strength decreases.
83
Where is the magnetic field strongest and weakest?
It is strongest near the poles and weakest near the center.
84
How can you find the strength of a magnetic field using iron filings?
Place the magnet on paper sprinkled with iron filings; the pattern shows the field strength.
85
How can you determine the direction of a magnetic field using needle compasses?
Place needle compasses at different positions around the magnet to observe the orientation of the needles.
86
How can the magnetic field produced by a current-carrying wire be increased?
* Increase the current/voltage
* Increase the length of the wire
* Move closer to the wire
87
How can the magnetic field from a coil be increased?
* Increase the current/voltage
* Increase the number of turns in the coil
* Use an iron core
## Footnote
Inside the coil the field lines are straight and parallel.
88
What are electromagnets and how do they operate?
* Electromagnets are magnets that can be switched on or off. When switch is closed, current passes through the coil and magnetizes an iron core (producing a strong field)
* When open, no current flows and no field occurs.
89
How can you increase the magnetic field of an electromagnet?
* Increase the current/voltage
* Increase the number of turns in the coil
* Use an iron core
90
What is a relay and how does it use magnetic fields?
* A relay uses a small current circuit to operate a circuit that uses a large current
* Closing the switch sends current through a coil, creating a magnetic field that attracts a free contact to close the circuit and power a motor.
91
What is the function of a circuit breaker in a circuit?
It uses the magnetic effect to reduce the current to its normal value when excess current flows through a wire in a magnetic field.
92
How can the magnetic force acting on a moving wire be increased?
* By increasing current/voltage
* By increasing the number of turns of the coil
* By using a stronger magnet
93
What causes a coil to rotate in a magnetic field?
Two equal and opposite forces (one acting downward on AB and one upward on CD) create a moment that rotates the coil.
94
How can you increase the speed of rotation of a coil?
* By increasing current/voltage
* By increasing the number of turns of the coil
* By using a stronger magnet
95
How can the direction of rotation of a coil be reversed?
* Reverse the current
* Reverse the poles of the magnet
96
What is the function of a DC motor?
A DC motor converts electric energy into kinetic energy.
97
What is the role of split ring commutators in a DC motor?
They reverse the direction of current every half cycle, ensuring that the coil rotates continuously in one direction.
98
What is the purpose of carbon brushes in a motor?
Carbon brushes connect the rotating coil with the battery.
99
How is an induced current generated?
When a wire moves inside a magnetic field, the rate at which magnetic lines are cut changes, inducing a current.
100
How can you increase the induced current (emf) in a wire?
* By increasing the length of the wire
* By increasing the strength of the magnets
* By moving the wire faster
101
What does Faraday’s law of induction state?
The induced emf is directly proportional to the rate at which magnetic field lines are cut by the wire.
102
What does Lenz’s rule state about the direction of induced current?
The induced current is opposite to the normal current.
103
Is the induced current produced by a moving wire AC or DC?
It is alternating current (AC).
104
How can the induced current (emf) in a coil be increased?
* By increasing the number of turns in the coil
* By increasing the strength of the magnets
* By rotating the coil faster
105
What is an AC generator and when is its maximum and minimum currents reached?
* An AC generator converts kinetic energy into electrical energy
* The current is zero when the coil is vertical and maximum when the coil is horizontal
106
What are slip rings in AC generators, and what are their function?
Slip rings are used in AC generators to provide a continuous transmitting of power (they aren't split in the middle)
107
What is mutual induction in electromagnetic induction?
It is the process by which a changing magnetic field in one circuit induces a current in a nearby circuit.
108
How does the movement of a magnet relative to a stationary coil affect induced current?
* When the magnet moves toward the coil, current is induced
* When it moves away, induced current occurs in the opposite direction
* If both move together at the same speed in same direction, no current is induced.
109
How does induced current occur when the coil moves relative to a stationary magnet?
* The coil moving toward the magnet induces a current, and moving away induces current in the opposite direction
* If both remain at rest, no induced current occurs.
110
How do transformers work?
By electromagnetic induction. When alternating current/voltage passes through primary coil it produces an alternating magnetic field. This magnetic field magnetises the iron core. The magnetic field transfers to the secondary coil using iron core. The rate of magnetic field lines cut changes by secondary coil so induced current/e.m.f. occur in secondary coil.
111
Why wouldn't a transformer work using DC?
A transformer wouldn't work using DC as rate of magnetic field lines cut wouldn't change
112
What is the relationship between primary and secondary coils in a transformer?
* Power is constant: 𝐼(𝑃) x 𝑉(𝑃) = 𝐼(𝑆) x 𝑉(𝑆)
* In step-up transformers: 𝑁(𝑃) < 𝑁(𝑆) so 𝑉(𝑃) < 𝑉(𝑆) and 𝐼(𝑃) > 𝐼(𝑆)
* In step-down transformers: 𝑁(𝑃) > 𝑁(𝑆) so 𝑉(𝑃) > 𝑉(𝑆) and 𝐼(𝑃) < 𝐼(𝑆)
113
Why is high alternating voltage used in the national grid instead of high alternating current?
1. To reduce current
2. To reduce heating effect
3. To reduce energy lost
4. Use thinner wires
5. Cheaper
6. Less metal used
7. Less insulating material used
114
Why are thick wires used to carry large current?
Thick wires are used to carry large current because they are more efficient, there is less, risk of fire, have a lower resistance so less energy lost, and because thin wires would melt due to heating effect
115
What are the key methods to increase magnetic effects in various devices?
* Increase current/voltage
* Increase the number of turns in coils
* Use stronger or iron cores
* Adjust proximity or movement speed
* When needed, reverse current or magnetic poles
116
What does the Right‑Hand Rule for Magnetic Fields around a straight wire state, and how do you use it?
Extend your **right thumb in the direction of the conventional current** (from positive to negative). **Your curled fingers then show the circular magnetic field lines around the wire**. Use this rule to determine the field direction around any straight current‑carrying conductor.
117
How is the Right‑Hand Rule for Magnetic Fields in Coils (Solenoids) applied, and what does it reveal?
**Curl the fingers of your right hand in the direction of the conventional current flowing through the coil loops.** **Your thumb will point in the direction of the magnetic field inside the coil**, indicating the north pole of the electromagnet. Use this rule to determine the polarity and field direction inside coils or solenoids.
118
What is Fleming’s Left‑Hand Rule (Motor Rule), and when should you apply it?
Hold your left hand so that **the thumb, forefinger, and middle finger are perpendicular. The index finger shows the direction of the magnetic field, the middle finger the direction of the current, and the thumb the direction of the force (motion) on the conductor.** Use this rule to predict the force direction on a current‑carrying conductor in electric motors.
119
Describe Fleming’s Right‑Hand Rule (Generator Rule) and its use in determining induced current direction.
Extend your right hand so that **your thumb points in the direction of the conductor’s motion relative to the magnetic field, your index finger points in the direction of the magnetic field, and your middle finger then indicates the direction of the induced current.** Use this rule when a conductor moves within a magnetic field, as in generators, to find the direction of the induced current.
120
Describe the magnetic field inside a solenoid.
* The magnetic field inside a solenoid is strong, uniform, and consists of straight, parallel lines.
* It resembles the field of a bar magnet, with distinct north and south poles at the ends.
