VCE Physics Question Thread!

[SocialRhubarb]

6b.) Calculate the impulse of the force provided by the burning gunpowder on the rocket.
It asks for the impulse generated by the 22N force alone. A separate impulse is provided by gravity and together they make up the resultant change in momentum of the rocket.

16a.) Doesn't specify a direction for the voltmeter. Both solutions should be correct.

18.) It's not a parallel circuit, it's a series circuit.

[Robert123]

Some Questions related to light and matter...
How does the medium (air vs water) influence the Fringe Spacing?


Electrons of known energy are fired into Mercury vapour. The energy of the scattered electrons is then measured. When electrons of energy from 0eV to 4.8eV are fired into the mercury vapour, the energy of the scattered electrons equal the energy of the incident electrons. At 4.8eV the energy of some of the scattered electrons falls to zero. Which of the following statements best explains this observation?
The answer is...
Inelastic collisions within the atoms can occur for electrons of energy 4.8eV, but not at lower energies.
Could someone please explain this to me.

For electronics...
If a diode with a turn on voltage of 0.7V is in parallel with a 6.0V battery as well as a resistor, what would be the voltage drop across the resistor? Would it matter whether the diode is in forward bias or reverse bias ?

And for electric power...
Also, are we meant to know how to work the EMF generated from a moving object in a constant magnetic field using EMF=BLv  as it was in the STAV 2013 practice exam?

Thanks

[lzxnl]

Some Questions related to light and matter...
How does the medium (air vs water) influence the Fringe Spacing?


Electrons of known energy are fired into Mercury vapour. The energy of the scattered electrons is then measured. When electrons of energy from 0eV to 4.8eV are fired into the mercury vapour, the energy of the scattered electrons equal the energy of the incident electrons. At 4.8eV the energy of some of the scattered electrons falls to zero. Which of the following statements best explains this observation?
The answer is...
Inelastic collisions within the atoms can occur for electrons of energy 4.8eV, but not at lower energies.
Could someone please explain this to me.

For electronics...
If a diode with a turn on voltage of 0.7V is in parallel with a 6.0V battery as well as a resistor, what would be the voltage drop across the resistor? Would it matter whether the diode is in forward bias or reverse bias ?

And for electric power...
Also, are we meant to know how to work the EMF generated from a moving object in a constant magnetic field using EMF=BLv  as it was in the STAV 2013 practice exam?

Thanks

Question 1:
Medium affects the speed of the wave. Frequency cannot change => wavelength changes. Fringe spacings affected.

Question 2:
I don't quite like how it says "energy falls to zero". Kinetic plus potential? I think the point is that if electrons from 0 eV to 4.8 eV are fired, they do not have enough energy to knock out another electron, so they just rebound back with the same energy. At 4.8 eV, some of the mercury bound electrons are given enough energy to just escape, so those electrons will have zero energy.

Diode question:
If it's in parallel, diode in forward bias takes 0.7 volts. So does resistor, as the voltage drops are the same in parallel circuits.
If the diode is reverse biased, no current flows through the diode. All current flows through the resistor instead. The diode essentially has infinite resistance. Voltage across diode is 6.0V, and so is the drop across the resistor.

As for electric power...it's just a formula, another what, two lines on your cheat sheet? Can't be that bad.

[BasicAcid]

As for electric power...it's just a formula, another what, two lines on your cheat sheet? Can't be that bad.

That's literally 7 characters (EMF=Blv)

The word commutator takes up more space than that lol

[lzxnl]

That's literally 7 characters (EMF=Blv)

The word commutator takes up more space than that lol

You'd need an explanation of what the formula is and what it means.

Oh wait, wrong subject.

[~T]

TSFX Exam 2 2010, Light and Matter question 3. Basically, photoelectric effect measured on a metal with blue light and with ultraviolet light. The graph of current vs. potential difference shows that blue light produces a higher current for the forward potentials.

Question 3 asks "which of the lights had a greater intensity?" with options "blue," "ultraviolet" or "unable to determine." The answers say "unable to determine" because the intensity of the light isn't the only determining factor in the current - higher kinetic energy will also make a higher current, and this depends on the frequency of the incident light.

I chose "blue", because the ultraviolet light will have higher energy photons - E=hf. It would need more photons to equal the photocurrent of the ultraviolet light, let alone produce a larger photocurrent. Right?

[~T]

Another question... we're doing the Synchrotron detailed study, and I was wondering: what dictates whether Thomson scattering, Compton scattering, or the photoelectric effect occurs when a photon interacts with an electron?

[lzxnl]

TSFX Exam 2 2010, Light and Matter question 3. Basically, photoelectric effect measured on a metal with blue light and with ultraviolet light. The graph of current vs. potential difference shows that blue light produces a higher current for the forward potentials.

Question 3 asks "which of the lights had a greater intensity?" with options "blue," "ultraviolet" or "unable to determine." The answers say "unable to determine" because the intensity of the light isn't the only determining factor in the current - higher kinetic energy will also make a higher current, and this depends on the frequency of the incident light.

I chose "blue", because the ultraviolet light will have higher energy photons - E=hf. It would need more photons to equal the photocurrent of the ultraviolet light, let alone produce a larger photocurrent. Right?

I can see the issues here. What we're used to dealing with is the MAXIMUM kinetic energy of the electrons, and that is given by hf-W. However, not all of the electrons are at this max value. At a certain voltage, all of the electrons do get to this max value, which is why we eventually see the graph smoothen out. Before this, however, varying proportions of electrons are not at this max value. We can only work out what the maximum energy is; we don't know the energy distribution of the electrons though.

[SocialRhubarb]

I chose "blue", because the ultraviolet light will have higher energy photons - E=hf. It would need more photons to equal the photocurrent of the ultraviolet light, let alone produce a larger photocurrent. Right?

If you have a laser shooting, say, 10000 photons of blue light per second, and a laser which is shooting 10000 photons of ultraviolet light per second, both on the same area, which laser has the higher intensity?

Well, the ultraviolet laser, since both the lasers emit the same number of photons, but the photons of ultraviolet light carry more energy per photon.

And that's really the issue here. Yes, from the graph we can tell that there are more photons of blue light being shone onto the metal. But intensity isn't only affected by the number of photons you shine, it's affected by the energy carried by each of those photons too. So while it is true that there are less photons of ultraviolet light, since each photon carries more energy than photons of blue light, it may be of a higher intensity, or lower intensity as well. It is unable to be determined.

[lolipopper]

question: attached

[lzxnl]

So...horizontal components of forces must be equal => tensions are equal as the angles are the same.
So now resolve vertical components.
2T*sin 25 = mg
T=mg/(2 sin 25). Whatever that is.

[lolipopper]

but the question says in the wire. so wont you multiply the answer by 2.

[lzxnl]

Is the top V-shaped thing one piece of wire?
If so...the tension will not be doubled. Even so. It's like one of those pulley questions. You could put a pulley there and it wouldn't change the force analysis.

[lolipopper]

whats the 2 for in the equation?

[lzxnl]

The string is split into two halves. Vertically, each half of the string contributes T sin 25 to the net force.