Quantum

Question 1

What is stopping potential used for ?

Answer 1

It is used to experimentally measure the Ke(max) of electrons as frequency is adjusted.

Question 2

What is the photoelectric effect ?

Answer 2

The photoelectric effect is caused when light incident on a metal surface causes electrons to emitted from the surface from the metal.

Question 3

What is expected to occur when electrons are used in double slit experiment and what actually happens ?

Answer 3

As electrons are particles you expect them to create two lines (like a stencil and paint)
but what actually happens is the electrons produce a diffraction pattern.

Question 4

What is a continuous spectrum ?

Answer 4

spectrum where all wavelengths are emitted.

Question 5

How do you convert J to eV ?

Answer 5

x/1.6x10^-19 (hint: value of eV is always a lot larger)

Question 6

Why are the electrons emitted with a range of Ke ?

Answer 6

Some electrons are embedded deeper in the surface of the metal so more E is required to escape.

Question 7

What is the work function ?

Answer 7

the minimum energy required to liberate an electron from the surface of a metal

Question 8

What is the threshold frequency of a metal ?

Answer 8

the threshold frequency is the minimum frequency of light incident on a metal surface needed to cause electrons to be emitted.

Question 9

For an electron to absorb energy and excite what must be the case ?

Answer 9

IT absorbs the exact amount of energy between the two energy levels. either a photon with exact energy of electron with E more than difference and leaves with difference of E as Ke.

Question 10

What is the formula linking Ek(max) and stopping potential.

Answer 10

Ek(max) = e V(stopping)

Question 11

What is the formula for the work function ?

Answer 11

Φ = h f0

Question 12

What is a emission line spectrum ?

Answer 12

When only specific wavelengths are emitted. (exciting hot gas)

Question 13

When f > f0 hat does increasing the brightness do ?

Answer 13

Increases the amount of electrons emitted per second.

Question 14

On a F Ek(max) graph what are the intercepts and gradient ?

Answer 14

X-int is threshold frequency
Y-int is work function
gradient is h plank constant (6.63x10^-34)

Question 15

What is the formula for de broglie wavelength and what is it ?

Answer 15

λ = h/p
de broglie wavelength is the effective wavelength of a particle.

Question 16

Explain how fluorescent lights work.

Answer 16

Current is passed through mercury gas which is at low pressure.
Atomic electrons gain E from incident electrons and excite then de-excite and emit UV.
Phosphor coating on light absorbs UV and atomic electrons excite and de-excite then emit visible light.

Question 17

Why must we think of light as a particle ?

Answer 17

The photoelectric effect cannot be proven when light is a wave.

Question 18

How do you work out Ke of a emitted electron ?

Answer 18

Photon energy = Φ + Ek

Question 19

What is a absorption line spectrum ?

Answer 19

When all wavelengths are emitted excluding specific frequencies. (continuous spectrum shone through cold gas)

Question 20

What is excitation ?

Answer 20

When an electron moves from low energy level to a higher.

Question 21

What is the relationship of frequency f photons and Ke of electrons ?

Answer 21

Higher frequency the higher Ke(max) of the electrons.

Question 22

What is a stopping potential circuit look like and how does it work ?

Answer 22

A photoemissive surface opposite a wire electrode in series with a cell and a ammeter (micro amp)
The negative terminal off cell points towards electrode, the electrons from the photoemisssive circuit oppose electrons from cell and when A = 0 the voltage of cell multiplied by e is equal to Ek(max).

Question 23

Why does increasing the brightness of the light not change anything when f>f0

Answer 23

Frequency is still under F0 so no change.

Question 24

What are the conditions for double slit for a particle to form a diffraction pattern ?

Answer 24

de broglie wavelength must be similar (within 100x) to slit separation.

Question 25

For an atom to be ionised what must be the case ?

Answer 25

E the electron absorbs must be greater than E between current energy level and greatest energy level.

Question 26

Explain the gold leaf experiment.

Answer 26

By touching a negatively charged rod to the plate the charge is transferred giving the stem a negative charge.
The stem and gold leaf then repel due to like charges.

When light is shone of the metal plate electrons are mitted due to the photoelectric effect. this removes the negative charge from the stem causing the gold leaf to attract to the stem.

Question 27

Describes bohrs model of the atom.

Answer 27

Electrons orbit nucleus in fixed orbits
When electron is in orbit it is at constant E
electron can only absorb and emit E when it excites/deexcited ?

Question 28

What are the three groups of emission spectrum of hydrogen gas ?

Answer 28

Lyman, Balmer, Paschen
lower λ ————> higher λ

Question 29

What is an electron volt ?

Answer 29

An electronvolt is the kinetic energy gained by one electron passing through a Pd of 1V.