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Physics > Random physics stuff I didn't previously have a flashcard for > Flashcards

Random physics stuff I didn't previously have a flashcard for

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1
Q

How has knowledge and understanding of EM radiation changed over time

A

End of 17th century - 2 theories published

Newton - light is composed of ‘corpuscles’ (tiny particles)

Huygens - light is composed of waves

Young’s double slit provided evidence for light as waves

Then later Einstein provided evidence for light as particles

Conclusion - it’s both

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2
Q

Applications of diffraction gratings

A

Used by chemists and astronomers to identify elements - more accurate than prisms

E.g. X-Ray crystallography and analysing the elements present in stars - split up light from a star to form a line absorption spectra

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3
Q

X-Ray crystallography

A

X-Rays are diffracted by the atoms of crystalline solids

Forms a diffraction grating

Atoms act as a diffraction grating

Used to identify elements

Used in the discovery of DNA structure

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4
Q

Out of phase

A

Destructive interference

Phase difference of pi radians or 180 degrees

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5
Q

Resonance, displacement and periodic force

A

Phase difference of 1/2 pi radians between displacement and periodic force

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6
Q

Differences between stationary waves and progressive waves

A

In a stationary wave points of a particular phase remain in the same location as time passes, but in progressive waves the points of the given phase travel forwards

In a stationary wave, no energy is transferred along the wave (from one point to another) it instead stores energy in ‘pockets’ whereas a progressive wave transfers energy

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7
Q

Stationary waves, nodes and antinodes for open ends and fixed (closed) ends

A

Open end -> antinode

Closed end -> node

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8
Q

SHM amplitude and displacement definitions

A

Displacement is the distance from equilibrium

Amplitude is maximum displacement

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9
Q

Brownian motion conclusions

A

Movement of smoke particles caused by collisions by randomly moving air molecules

Smoke particles are visible but air molecules are not hence air molecules must be very small

Small movement of smoke particles is due to the large number of air molecules from all sides

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10
Q

Boyle’s law definition

A

Pressure is inversely proportional to volume for a fixed mass of gas at a constant temperature

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11
Q

Single slit diffraction pattern

A

Wider central maximum surrounded by other lower intensity maxima with dark minima between maxima

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12
Q

Impact of increasing wavelength on diffraction pattern

A

Larger fringe spacing

Wider central maxima

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13
Q

Impact of using a light source which emits a range of wavelengths on the interference pattern

A

Central maxima unchanged in width (depending on the range)

Broader maxima and maxima get even broader as order increases

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14
Q

Equation for calculations involving mol

A

N = nNa

N is number of atoms
n is number of moles
Na is Avagadro’s constant

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15
Q

Widths of central maximum

A

Increasing slit width decreases the amount of diffraction - decreases width of central maximum (gets narrower) and increases its intensity

Increasing wavelength increases diffraction - central maximum is wider and intensity is lower

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16
Q

Phase difference for two points on the same wave

A

The phase difference of two points on a wave is the difference in their positions in the wave’s cycle

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17
Q

Resonant frequencies on a string - stationary waves

A

A frequency at which a stationary wave is formed because an exact number of waves are produced in the time it takes for a wave to get to the end of the string and back again

An exact number of half wavelengths fit on the string

The string vibrates at maximum amplitude

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18
Q

Observing stationary waves using sound waves and microwaves

A

Use a loudspeaker to direct sound waves into a glass tube with a flat end to reflect them, put powder in the tube and it will collect at the nodes

Use a metal plate to reflect microwaves and a probe to observe the nodes and antinodes

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19
Q

Why does f decrease when L increases

A

The harmonic frequencies correspond to the number of half wavelengths on a string

If the length is increased, the wavelength of the resonant frequency would also increase

Speed of the wave must remain constant so f must increase

Can also use the formula for the first harmonic to reason this

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20
Q

Why is a laser better than white light for producing a clear diffraction pattern?

A

Laser light is monochromatic - all the same wavelength, all diffract by the same amount giving sharp, bright fringes

White light is made up of a range of wavelengths which diffract by different amounts

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21
Q

How to create coherent sources of sound waves and light

A

Connect two loudspeakers to a single amplifier

Direct monochromatic light into a double slit

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22
Q

Investigating the interference and diffraction pattern of sound waves and microwaves

A

Attach two loudspeakers to an amplifier and create sound waves at a set frequency, walk along a straight line parallel to the line of the speakers and mark the minima and maxima

Same for microwaves except using microwave emitters and a probe

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23
Q

Change in direction at material boundaries

A

If light is passing into a more optically dense material then it moves towards the normal

If light is moving into a less optically dense material then it moves away from the normal

24
Q

Requirements for TIR

A

Light is passing from a more optically dense medium into a less optically dense medium

The incident angle of the light exceeds the critical angle

25
Q

Relative refractive index

A

The ratio of the speed of light in material 1 to the speed of light in material 2

= C1 / C2 = n2 / n1

26
Q

Absolute refractive index

A

The ratio between the speed of light in a vacuum, c, and the speed of light in the material, cs

n = c/cs

27
Q

Advantages of optical fibres over old system (copper cables)

A

The signal can carry more information because light has a high frequency

The light doesn’t heat up the fibre - almost no energy is lost as heat

No electrical interference

Fibre-optic fibres are much cheaper to produce

The signal can travel a long way, very quickly and with minimal signal loss

28
Q

Energy transfers in an oscillating spring SHM

A

Kinetic energy - minimum at A and max at equilibrium

GPE - Increases as mass rises from highest to lowest point

Elastic energy - decreases as mass rises from highest to lowest point

Unless its theoretical then for a pendulum or a spring energy is transferred to the surroundings due to air resistance

29
Q

When temperature increases:

When a substance is changing state:

A

KE increases and PE increases (But mainly KE)

KE remains constant and PE increases

30
Q

Extra things to know about conservation of momentum

A

Conserved when no external forces act and when the mass of the system remains constant

31
Q

Definition of wave speed

A

Speed at which energy is transferred
Speed of the wavefront
The distance travelled by the wave in a given time

32
Q

What affects Crms of molecules?

A

The ONLY thing that will affect Crms is temperature

33
Q

Effect of light intensity on LDR?

Effect of increasing temperature on a thermistor?

A

Resistance decreases

Resistance decreases

34
Q

Couple

Moment of a couple

A

Pair of equal and opposite coplanar forces

Defined as force x perpendicular distance between the lines of action of the forces

35
Q

Why does a photoelectron emitted from deeper within the metal have a lower kinetic energy than one emitted from the surface?

A

The electron has to do work to reach the surface

36
Q

Cloud chamber

A

Can be used to identify ionising radiation based off the length and shape of the path followed

37
Q

What happens to the frequency when using large tensions for the stationary waves on a string experiment?

A

Diameter of the string is reduced due to the extension of the string

This results in a lower mass per unit length

So frequencies would be higher than expected

38
Q

Double slit interference experiment, but one of the slits is then closed, what is the effect on the resulting interference pattern?

A

Fewer maxima are observed

39
Q

A wire has young modulus, E

A second wire made from identical material has 3 times the length and half the diameter, what is it’s young modulus in terms of E?

A

E

Remember Young modulus is a constant property of a material!!!

40
Q

Conditions for the formation of stationary waves

A

Two progressive waves moving in opposite directions

Waves must have the same frequency

Waves must have the same/or similar amplitude

41
Q

What are the differences between a diffraction pattern formed by white light compared to one formed by red light?

A

Central maximum would be white

The maxima would be continuous spectra with violet closest to the central maxima

The fringe spacing would be smaller due to the average wavlength of white light being less than that of red light

The bright fringes (maxima) are wider and the dark fringes are narrower

42
Q

Difference between emf and potential difference

A

EMF is the energy transferred per unit charge passing through the source whereas pd is the energy transferred per unit charge between two points

43
Q

How do springs used as dampeners reduce the oscillations of a bridge? Why must they be critically damped?

A

Springs absorb energy from the bridge

Springs oscillate with the natural frequency of the bridge

There is energy transfer from the bridge to the springs

Springs must be critically damped so the don’t return any energy back to the bridge - the damping ensures the energy is dissipated

44
Q

Why might the spacing between the first orders and the zeroth order be uneven?

A

The screen may not be parallel to the grating

The incident light may not be normal to the grating

45
Q

Why does having a rotating turntable on a microwave reduce uneven heating of the food?

A

The food rotates moving through nodes and anti nodes such that overtime all parts of the food receive a similar amount of energy

46
Q

Displacement of a wave

A

How far a point on a wave has moved from the its undisturbed position

47
Q

When is the normal contact force maximum and minimum when considering circular motion in a vertical plane?

A

ask mr simpson

48
Q

Which is better for determining wavelength: young’s double slits or diffraction grating?

A

Diffraction grating:

As the fringes are sharper and likely to be wider spaced resulting in a lesser percentage uncertainty

49
Q

How can you experimentally determine whether or not two points on a stationary wave are in phase or out of phase?

A

Use a video camera to record the stationary wave when it is in motion

If in they are in phase then the two waves will move up and down together

If they are out of phase then one wave will be moving up whilst the other wave moves down

50
Q

What happens to the diffraction pattern if you increase the amplitude of the waves incident on the double slits?

A

No change to dark fringes

No change in fringe separation or fringe width

Bright fringes get brighter/more intense

51
Q

How does the electron diffraction experiment support the idea that electrons behave as waves?

A

Particles would scatter randomly

Graphite acts as a diffraction grating

Diffraction is a property of waves

Bright fringes represent in phase/ constructive interference

Dark fringes represent out of phase/destructive interference

52
Q

How does electron diffraction experiment show electrons behaving as particles?

A

Electrons collide with the screen causing emission of photons

Electrons can’t be behaving like particles as emission is instantaneous and it would take time to absorb waves

53
Q

Stationary waves

A

Superposition of two waves travelling in opposite directions

Constructive interference forms nodes

Destructive interference forms antinodes

Fixed boundaries are nodes

Waves have same frequency and similar amplitude

54
Q

When does light move towards or away from the normal?

A

Moving into a more optically dense medium - refracts towards the normal

Moving into a less optically dense medium - refracts away from the normal

55
Q

Role of the cladding of an optical fibre

A

protects from scratches

avoids cross talk - keeps the core away from adjacent fibres

helps reduce signal loss

needed for TIR as it has a lower refractive index than the core

56
Q

Explain why the resistance of a NTC thermistor decreases as temperature rises

A

Increased temperature releases electrons - they have sufficient energy to leave the atom

Current therefore increases as the number of charge carriers increases

The effect of increased charge carriers has more effect than the effect of more collisions with the lattice

Physics (22 decks)

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