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NSAA > Part B > Flashcards

Part B Flashcards

1
Q

P1.1 What are insulators?

A

Insulators do not readily conduct electricity but can be charged by friction due to the gain or loss of electrons.
Some characteristics that increase the generation of electrostatics are low material conductivity, impurities, large contact surface, high speed of separation, high velocity, and low air humidity.

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2
Q

P1.1D What are the applications and hazards of electrostatics?

A

Electrostatic sparks caused by the flow of electrons between two conductors may have enough energy to produce electric shocks, cause electronic damage, spoil mechanical components, disrupt production processes, and generate fires and explosions. But static electricity has practical applications like electrostatic precipitators, photocopiers, printers, and Van de Graaff generators.

One effective way of preventing sparks is by connecting all objects to a conductor (bonding) and to the earth (grounding).
Bonding is a secure joining of metallic parts that form an electrically conductive path, dropping their voltage difference to near zero. Yet, there may be a voltage difference relative to the ground or another object. Bonding prevents sparks from jumping between two things that are at the same potential.
Grounding is a connection between the objects and the earth, allowing the discharge of electrostatic electricity to the ground.

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3
Q

P1.2.A Basic circuit symbols: cell, battery, light source, resistor, variable resistor, ammeter, voltmeter, switch, diode.

A
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4
Q

P1.2.B What is the difference between direct and alternating current?

A

In direct current, the electric charge only flows in one direction.
In alternating current, the electric charge changes direction periodically.

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5
Q

P1.2.C What are the differences between conductors and insulators?

A

Conductors (metals, aqueous solutions of salts, graphite, the human body) are materials which allow electrons to flow freely through them.
Insulators (plastics, styrofoam, paper, rubber, glass, dry air) resist the flow of electrons, so do not allow electric current to pass through them.

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6
Q

P1.2.D What is the equation linking time, current and charge?

A

current (A) = charge (C) / time (s)

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7
Q

P1.2.F What is the equation linking voltage, resistance and current?

A

voltage (V) = current (A) x resistance (Ω)

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8
Q

P1.2.G What are the I-V (take care with axes) graphs for filament bulbs and fixed resistors?

A

Filament bulbs: positive exponential going through (0,0), as current increases the temperature increases so the resistance goes from low to high thereby increasing the gradient as the proportional increase in voltage decreases.
Fixed resistors: straight line going through (0,0) as it is an ohmic conductor so voltage is directly proportional to current.

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9
Q

P.1.2.H What are NTC thermistors, LDRs and ideal diodes?

A

NTC thermistors: resistors with a negative temperature coefficient, which means that the resistance decreases with increasing temperature.
LDRs: resistors which have decreasing resistance with increasing light intensity.
Ideal diodes: a diode that acts like a perfect conductor when voltage is applied forward biased and like a perfect insulator when voltage is applied reverse biased to control the direction of current.

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10
Q

P1.2.I What are the current and voltage rules for series and parallel circuits?

A

In series: current is constant in all parts of the circuit. It can be calculated by dividing the total voltage of the battery or cell by the total resistance in the circuit. Total voltage is shared amongst components. The higher the resistance of an individual component, the greater its share of the voltage so that current stays constant everywhere.

In parallel: current is split between branches proportionally to their resistance where a higher resistance has a lower current. The sum of the currents of all branches is equal to the total current that flows from the power source. The voltage is the full maximum value for all components.

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11
Q

P.1.2.JK How does resistance act in series and parallel resistors?

A

In series: the total resistance is equal to the sum of the resistances of the components. Rt = R1 + R2 + …
In parallel: The total resistance is less than any individual component. 1/Rt = 1/R1 + 1/R2 + …

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12
Q

P.1.2.L What is the equation linking charge, voltage and energy?

A

voltage (V) = energy (J) / charge (C)

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13
Q

P.1.2.M What is the equation for power?

A

power (W) = voltage (V) x current (A) = current^2 (A^2) X resistance (Ω) = voltage^2 (V^2) / resistance (Ω)

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14
Q

P.1.2.N What is the equation linking power, energy transferred, and time?

A

energy transferred (J) = power (W) x time (s)

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15
Q

P.2.1.B What is the magnetic field pattern around a bar magnet?

A

They are continuous closed curves going from north to south pole. They are crowded where the magnetic field is strong, near the poles.

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16
Q

P.2.1.C What are hard and soft magnetic materials?

A

Hard: a substance which is permanently magnetised.
Soft: a substance which is temporarily magnetised.

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17
Q

P.2.1.D What is induced magnetism?

A

The process where any unmagnetised object gains temporary magnetic capabilities when it is put inside the magnetic field of any magnet.
Induced magnets need another source of the magnetic field to get magnetised, their magnetism is temporary, they can only be attracted by other magnets, and are much weaker than permanent magnets.

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18
Q

P.2.2.A What is the magnetic effect of a current?

A

When an electric current flowing in a wire produces a magnetic field around it.

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19
Q

P.2.2.B What are the magnetic field patterns around coils, solenoids and straight wires?

A

Coils: concentric circles which almost become parallel in the centre.
Solenoids: the same as those around bar magnets.
Wires: concentric circles going in the direction of the fingers when the right hand thumb points in the direction of the current.

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20
Q

P.2.2.C What factors affect the magnetic field strength around a wire?

A

The magnitude of the electric current and the perpendicular distance between the point and the conductor.

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21
Q

P.2.2.D What are the differences between magnets and electromagnets?

A

Electromagnets produce a magnetic field when a current flows through them.
The magnets poles can be changed and the field strength can be changed.

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22
Q

P.2.3.A What happens when a current carrying wire is in a magnetic field?

A

A force is produced.
If the wire is parallel to the magnetic field, there will be no force. If the wire is perpendicular to the magnetic field then the force will be maximum.

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23
Q

P.2.3.B What factors affect the direction of a force on a wire in a magnetic field?

A

The orientation of the poles of the magnet.
The left hand rule: display hand as though the three fingers are the three axes.
Thumb - thrust force
Second finger - field
Third finger - current

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24
Q

P.2.3.C What factors affect the strength of a force on a wire in a magnetic field?

A

The speed at which the wire, coil or magnet is moved: increasing the speed will increase the rate at which the magnetic field lines are cut. This will increase the induced potential difference.
The number of turns on the coils in the wire: increasing the number of turns on the coils will increase the potential difference induced because each coil will cut through the magnetic field lines.
The size of the coils: increasing the area of the coils will increase the potential difference induced because there will be more wire to cut through the magnetic field lines.
The strength of the magnetic field: increasing the strength of the magnetic field will increase the potential difference induced.

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25
Q

P.2.3.D What equation can be used to find the force of a straight wire at right angles to a uniform magnetic field?

A

force = magnetic field x current x length of conductor

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26
Q

P.2.3.E What is a dc motor?
Not done

A

A DC motor converts electrical energy input into the mechanical energy output.

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27
Q

P.2.4.A How can a voltage be induced by a magnetic field?

A

By a wire cutting the magnetic field lines or when a magnetic field changes.

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28
Q

P.2.4.D How does an ac generator work?

A
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29
Q

P.2.4.E

A
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30
Q

P.2.4.F

A
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31
Q

P.2.5.A

A
32
Q

P.2.5.B

A
33
Q

P.2.5.C

A
34
Q

P.2.5.D

A
35
Q

P.3.1.D What is a simple equation for acceleration?

A

acceleration = change in velocity / change in time

36
Q

P.3.1.H A suvat equation?

A

v^2 - u^2 = 2as

37
Q

P.3.3.A What do force extension graphs represent?

A

The gradient is k. The limit of proportionality is the point at which when the load is increased any further, the spring will not obey Hook’s Law.

38
Q

P.3.3.B What is elastic and inelastic extension and the elastic limit?

A

Elastic extension: extension which is completely reversed once the deforming force has been removed.
Inelastic extension: extension which is not completely reversed when the deforming force has been reduced.
Elastic limit: the point at which when the load is increased any further the spring will not return to it’s original length when the load is removed.

39
Q

P.3.3.C What equation can be used up to the limit of proportionality?

A

Hook’s Law: F = kx

40
Q

P.3.3.D What is the equation for the energy stored in springs?

A

E = 1/2 Fx = 1/2 kx^2

41
Q

P.3.4.A What is Newton’s first law?

A

A body will remain at rest or in a state of uniform motion in a straight line unless acted on by a resultant external force.

42
Q

P.3.4.B How does mass affect inertia?

A

The tendency of an object to resist changes in its state of motion varies with mass. Mass is that quantity that is solely dependent upon the inertia of an object. The more inertia that an object has, the more mass that it has. A more massive object has a greater tendency to resist changes in its state of motion.

43
Q

P.3.4.C What is newton’s second law?

A

F = ma

44
Q

P.3.4.D What is newton’s third law?

A

Every action has an equal and opposite reaction.

45
Q

P.3.5.E What are the factors affecting air resistance?

A

Speed, cross-sectional area and the density of the air. Air densities vary with altitude, temperature and humidity.

46
Q

P.3.6.AB What is the equation for momentum?

A

momentum = mass x velocity
Momentum is always conserved.

47
Q

P.3.6.C What is the equation linking force and moemntum?

A

Force = rate of change of momentum

48
Q

P.3.7.AB What is work done?

A

Work done is a transfer of energy.
work done (J) = force (N) x distance moved (m)

49
Q

P.3.7.C What is an equation for gravitational potential energy?

A

GPE = mgh

50
Q

P.3.7.D What is an equation for kinetic energy?

A

KE = 1/2 mv^2

51
Q

P.3.7.E What is an equation for power in a mechanical sense?

A

power = energy transferred / time taken

52
Q

P.4.1.A What are thermal insulators and conductors?

A

Conduction is usually faster in certain solids and liquids than in gases as the particles are closer together. Metals are especially good thermal conductors because they have freely moving electrons that can transfer thermal energy quickly and easily. Air is an especially good insulator.

53
Q

P.4.1.B What are the factors affecting the rate of conduction?

A

Thermal conduction occurs when particles with more thermal energy collide with particles with less thermal energy and transfer some of that energy.
The rate of conduction is proportional to the temperature difference, cross-sectional surface area, time and 1/length.

54
Q

P.4.2.A How does temperature affect the density of fluids?

A

When a fluid is heated, its particles gain more kinetic energy so can spread out, thereby becoming less dense, so they will rise above the cooler fluid.

55
Q

P.4.3.A What is thermal radiation?

A

Electromagnetic waves in the infrared region.

56
Q

P.4.3.C What factors affect the rate of absorption and emission?

A

Colour, reflectivity (rough or smooth), temperature, and surface area.

57
Q

P.4.4.B What is the equation for the specific heat capacity?

A

specific heat capacity = thermal energy / mass x temperature change

58
Q

P.5.2.A How does particle behaviour explain temperature and pressure?

A

As the temperature increases, the average kinetic energy increases as does the velocity of the gas particles hitting the walls of the container. The force exerted by the particles per unit of area on the container is the pressure, so as the temperature increases the pressure must also increase.

59
Q

P.5.2.B What is true about the volume and pressure of a gas if the temperature remains the same?

A

pressure x volume = constant

60
Q

P.5.3. What do the terms latent heat of fusion and latent heat of vaporisation mean?

A

Latent heat of fusion: the amount of energy needed to melt or freeze a material at its melting point.
Latent heat of vaporisation: the amount of energy needed to condense or boil a material at its boiling point.

61
Q

P.5.3.C What is the equation for the latent heat energy?

A

energy required to change state = l (specific latent heat of the substance) x mass

62
Q

P.5.4.A What is the equation for density?

A

density = mass / volume

63
Q

P.5.5.A What is the equation for pressure?

A

pressure = force / area

64
Q

P.5.5.B What is the equation for hydrostatic pressure?

A

pressure = fluid density x fluid depth x g

65
Q

P.6.1.F What equation links frequency and time period?

A

frequency = 1 / time period

66
Q

P.6.1.H What is an equation for wave speed?

A

wave speed = frequency x wavelength

67
Q

P.6.2.C How does reflection and refraction change the speed, direction, frequency, wavelength and direction of waves?

A
68
Q

P.6.2.D What is the analogy of reflection and refraction of light with that of water waves?

A
69
Q

P.6.3.B What’s a nice little fact about the angles in reflection?

A

angle of incidence = angle of reflection

70
Q

P.6.3.D What’s a nice little fact about the angles in refraction?

A

n1sin(x1) = n2sin(x2)

71
Q

P.6.3.E How does refraction affect wave direction and speed?

A

When a wave passes from a material of low optical density to high optical density it slows down and changes direction towards the normal.
When a wave passes from a material of high optical density to low optical density it speeds up and changes direction away from the normal.

72
Q

P.6.4.F What is the range for human hearing?

A

20-20,000 Hz

73
Q

P.6.4.G What are the uses of ultrasound?

A

Sonar and medical scanning: the waves are reflected at the boundary, the time taken for the waves to leave a source and return to a detector is measured and the depth of the boundary can be determined using d=s/t.

74
Q

P.6.5.CD What are the respective frequencies and wavelengths of the different regions of the EM spectrum?

A

wave speed = frequency x wavelength
Radio: 100km
Micro: 10cm
IR: 10,000nm
Visible light: 700nm - 400nm
UV: 100nm
X-rays: 10nm
Gamma: 1 x 10^-6 nm

75
Q

P.7.3.ABC What is the relative range, ionising ability and deflection in magnetic fields of the different radiation particles?

A

Alpha: 3-5 cm, highly ionising, deflects towards the negative plate.
Beta: 15 cm, ionising, deflects towards the positive plate.
Gamma: very length, weakly ionising, does not deflect. (stopped by 5cm of lead)

NSAA (5 decks)

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