El;ectrons waves and photons corrections Flashcards

(20 cards)

1
Q

Explain how the I-V characteristic show how the resistivity of a semiconductor decreases with increasing temperature

A

(graph curves so) R changes qualification: I increases faster than V

increased temperature is caused by (larger) current in slice qualification: P = I2R as R decreases ρ decreases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

How does the p.d across the resistor vary as the intensity of the light on a LDR increase

A

total R falls so I in circuit/in R1 increases so V across R1 increases and V across 750 Ω falls

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Define the photoelectric effect

A

emission of electron(s) from a metal (surface) when photon(s)/ light/uv/em radiation are incident (on surface)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

The SI unit of energy

A

J

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Explain why a double slit is used instead of two identical light sources

A

light from the two sources must be/slits is coherent only possible to produce constant phase difference using a single source

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Use of LEDS and positives

A

torch; car brake/rear light/ traffic light, etc. torch: draws a lower current / light lasts longer before battery discharged/AW or LEDs (much) more efficient (at converting electrical energy into light)/AW or if one LED fails remainder still lit/AW

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

why do electron transitions between the energy levels produce different wavelengths

A

(atom releases energy when) electron moves from high to
low level
energy released is in form of a photon
possible transitions are between n = 3 and n = 1, n = 3
and n = 2, n = 2 and n= 1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How to find the separation of the lines on the grating

A

dsin$= lamda

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

how to calculate the number of lines per mm on the grating

A

1/d

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Properties of em waves

A

travel in a vacuum
same speed (in vacuum)/at c
caused by accelerating charges
are (oscillating) electric and magnetic fields

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

How to calculate energy gained by an electron

A

E=eV

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

How does the resistance of the filament lamp change with time

A

the resistivity/resistance of the (metal) filament increases with temperature the larger the current in the filament the hotter it becomes/AW

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Plane polarised wave

A

oscillations (of particles/e-m fields along the wave) are in one direction only perpendicular to the direction of wave propagation/of travel of the wave/of energy transfer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How are work function and threshold frequency related

A

a photon with less than the threshold frequency f0 cannot cause electron emission/AW so work function = h (threshold frequency)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Define the photoelectric effect

A

The emission of electrons from the surface of a metal when electromagnetic waves (of frequency greater than the threshold frequency) are incident on the metal.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Explain how the photoelectric effect cant be explained by the wave model of em waves but it validates the photon model

A

The wave model cannot explain why there is a threshold frequency for metals.

The new model / photon model proposed one-to-one interaction between photons and electrons and this successfully explained why threshold frequency exists.

Any further one from: Energy of photon (hf) must be greater than or equal to work function of metal. The kinetic energy of emitted electrons was independent of the incident intensity. Correct reference to hf = Φ + KEmax

17
Q

State the effect intensity has on em radiation

A

The energy of a photon depends only on wavelength or frequency, so intensity does not change the maximum speed of the photoelectrons.

18
Q

Determine how time constant can be determined

A

Connect a voltmeter or data-logger or oscilloscope across the resistor (or capacitor) or an ammeter in series with the resistor.

A stopwatch is started when the switch is opened and stopped when the p.d. or the current to decreases to 37% of its initial value.

The time constant is the time taken for the p.d. or the current to decreases to 37% of its initial value.

19
Q

Calculating half thickness of lead

A

Equipment (E) 1. GM tube, counter or rate-meter and lead plates used 2. Micrometer or vernier calliper (to measure thickness of plates).

Description (D) 1. Measure counts for a specific time and hence the count-rate for each thickness of lead 2. Vary the thickness of lead and record the count-rates 3. Plot a graph of count-rate against thickness and determine the half thickness of lead 4. Fig. 23.1 is used to determine the photon energy.

Safety (S) 1. Do not point source at person 2. Keep safe distance between you and source 3. Use tongs to handle source.

Quality of results (Q) 1. The counts are recorded over a long period of time 2. Background radiation taken into account.

20
Q

Discuss ethical issus the use of PET scanners have

A

Doctors have to make difficult decisions about who can and cannot have a PET scan.

Some patients will miss out on PET scans because of their location / not all patients will have access to the scans.