HSC Physics Question Thread

[Shadowxo]

hiii pls help :/
a 60pkg drag car completes the 400m with a final speed of 200kmhr. whats the net force on the car assuming the acceleration of the car is constant

my teacher used the fact that v+u/2 =average velocity

Hi
So, as the acceleration is constant, the average velocity would in fact be (u+v)/2, but I'd recommend using a different formula
You know u =0, v=200/3.6 m/s , s=400m and you want to know a.
Use v²=u²+2as to find a, then F=ma to find the force

[itssona]

Hi
So, as the acceleration is constant, the average velocity would in fact be (u+v)/2, but I'd recommend using a different formula
You know u =0, v=200/3.6 m/s , s=400m and you want to know a.
Use v²=u²+2as to find a, then F=ma to find the force

ohh!! thank you sooo much!!

[julies]

hey there =)
Would someone be able to explain how forward biased p-n junctions work?
I don't understand how the depletion zone decreases when the positive terminal is connected to the p type and the negative terminal is connected to the n type...

[austv99]

What are the ideal radioisotopes for this dotpoint (Quanta to Quark)?
"describe some medical and industrial applications of radio-isotopes
identify data sources, and gather, process, and analyse information to describe the use of: – a named isotope in medicine – a named isotope in agriculture – a named isotope in engineering"
Is Cobalt-60 for Agriculture or Engineering?

I'm confused on how Heisenberg and Pauli contributed to atomic theory

Can anyone clarify this?

Mod edit: Merged posts

[kiwiberry]

What are the ideal radioisotopes for this dotpoint (Quanta to Quark)?
"describe some medical and industrial applications of radio-isotopes
identify data sources, and gather, process, and analyse information to describe the use of: – a named isotope in medicine – a named isotope in agriculture – a named isotope in engineering"
Is Cobalt-60 for Agriculture or Engineering?

I'm confused on how Heisenberg and Pauli contributed to atomic theory

Can anyone clarify this?

Mod edit: Merged posts

Hey! Co-60 is used in agriculture for food irradiation. For medicine, Tc-99m (used in diagnostic imaging) is probably the best one to use. For engineering, you could use Na-24 (used to detect leaks) or Ir-192 (used to detect structural faults).

Heisenberg developed matrix mechanics, which was a completely mathematical model of the atom - this was able to provide an explanation of the limitations of Bohr's model (different intensities of spectral lines, hyperfine lines, Zeeman effect, emission spectra of atoms larger than H) and more. He also proposed the uncertainty principle, which states that there is a fundamental limit to how accurately an electron's position and momentum can be determined:

Pauli proposed the exclusion principle, which states that no two electrons can have the same 4 quantum numbers (principle, orbital, magnetic, spin) - this explained the electron distribution in atoms and the position of elements in the periodic table. He also proposed the existence of the neutrino to explain the differing energies of beta decay.

Hope this helps!

[jamonwindeyer]

hey there =)
Would someone be able to explain how forward biased p-n junctions work?
I don't understand how the depletion zone decreases when the positive terminal is connected to the p type and the negative terminal is connected to the n type...

Hey! This is right on the borderline of what you are expected to know, but roughly:

- When you connect a voltage source such that the positive terminal is connected to the P-type, and the negative terminal is connected to the N type, this pushes the positive holes in the P-type towards the junction, and the negative electrons in the N-type towards the junction. This is a forward bias connection. This reduces the size of the depletion region. Another way to think of it is that the applied voltage sort of 'cancels' the potential difference caused by the depletion region in the first place. This allows current to flow!
- If we connect it the other way around, the opposite occurs! We don't take away from the voltage, we make it worse, so to speak! This increases the size of the region and thus makes it very difficult for current to flow. Practically, eventually, you would get current - It happens when the diode goes "nope" and electrons start being ripped away from their atoms. But this is reverse bias, essentially a no current scenario!

[blasonduo]

Hello, this was the multiple choice question I got wrong in my trial paper, could you please help?

An AC motor, when COMPARED to a DC motor:

a) will spin at a rate determined by the electricity supply frequency.
b) will spin at a rate determined by the electricity supply voltage.
c) will produce more torque than a similar DC motor.
d) will spin faster than DC motor.

thanks

[winstondarmawan]

Hello! Would appreciate help with the following:
7. https://scontent-syd2-1.xx.fbcdn.net/v/t35.0-12/21267582_1313522785439908_359337286_o.png?oh=e3810f91e5c593c5ebdcbd6cb50703e5&oe=59AA295D
15. https://scontent-syd2-1.xx.fbcdn.net/v/t34.0-12/21245454_1313523275439859_1895111845_n.png?oh=cfd8d8d15289dc9308a4256bd8c2a820&oe=59AA21CC
Quanta to Quarks:
https://scontent-syd2-1.xx.fbcdn.net/v/t34.0-12/21268713_1313673448758175_1133813723_n.png?oh=0122454ffa0cd5e02612106c8e5c44f6&oe=59AB27C9
Thanks in advance!

[jamonwindeyer]

Hello, this was the multiple choice question I got wrong in my trial paper, could you please help?

An AC motor, when COMPARED to a DC motor:

a) will spin at a rate determined by the electricity supply frequency.
b) will spin at a rate determined by the electricity supply voltage.
c) will produce more torque than a similar DC motor.
d) will spin faster than DC motor.

thanks

Hey! Before I explain it, I want to make sure I'm correct because I'm not 100% on how to interpret it - Is the answer A?

[jamonwindeyer]

Hello! Would appreciate help with the following:
7. https://scontent-syd2-1.xx.fbcdn.net/v/t35.0-12/21267582_1313522785439908_359337286_o.png?oh=e3810f91e5c593c5ebdcbd6cb50703e5&oe=59AA295D
15. https://scontent-syd2-1.xx.fbcdn.net/v/t34.0-12/21245454_1313523275439859_1895111845_n.png?oh=cfd8d8d15289dc9308a4256bd8c2a820&oe=59AA21CC
Quanta to Quarks:
https://scontent-syd2-1.xx.fbcdn.net/v/t34.0-12/21268713_1313673448758175_1133813723_n.png?oh=0122454ffa0cd5e02612106c8e5c44f6&oe=59AB27C9
Thanks in advance!

Hey! Q7, Weber is Magnetic Flux, related to flux density by the formula:



The units on the RHS there are \(T\) and \(m^2\), so the answer is C

For Q15, the change in voltage between the plates is linear. The proton is two thirds the distance from the bottom plate that the top plate is, so the answer is \(\frac{2}{3}\times600=400V\)

Hopefully someone who did Quanta can jump in for the last one

[blasonduo]

Hey! Before I explain it, I want to make sure I'm correct because I'm not 100% on how to interpret it - Is the answer A?

Yes sir

[jamonwindeyer]

Yes sir

Cool - So we know that in an AC Motor, the changing direction of current is what maintains the constant direction of torque (the job that the split ring commutator does in a DC motor). What this means is that the AC frequency (how fast it switches) will determine how quickly the motor will spin. It will complete one half spin, then the current will switch direction, so it can complete another half spin, and so on. In a DC motor, it is purely the size of the current that determines how quickly it will spin - In an AC motor this is more or less irrelevant, because the frequency will apply the strictest conditions on its motion!

It's a little hard to explain admittedly, does that make sense though?

[kiwiberry]

Quanta to Quarks:
https://scontent-syd2-1.xx.fbcdn.net/v/t34.0-12/21268713_1313673448758175_1133813723_n.png?oh=0122454ffa0cd5e02612106c8e5c44f6&oe=59AB27C9
Thanks in advance!

Hey there! de Broglie hypothesised that all moving particles have a wave nature with wavelength given by \(\frac{h}{mv}\). I reckon they want you to talk about Davisson and Germer's experiment and how it provided support for de Broglie's proposal. So D&G fired electrons onto annealed nickel, and found that they produced a diffraction pattern - diffraction is a wave property, so they were able to show that electrons also have a wave nature. Using this pattern and Bragg's equation they were able to calculate the electron's wavelength, and this corresponded to that predicted by de Broglie's equation \(\lambda = \frac{h}{mv}\). Thus, D&G's experiment provided support for de Broglie's hypothesis and led to the new matter-wave theory. I definitely think this question should be worth more than 2 marks haha - hope this helps!

[winstondarmawan]

Hey there! de Broglie hypothesised that all moving particles have a wave nature with wavelength given by \(\frac{h}{mv}\). I reckon they want you to talk about Davisson and Germer's experiment and how it provided support for de Broglie's proposal. So D&G fired electrons onto annealed nickel, and found that they produced a diffraction pattern - diffraction is a wave property, so they were able to show that electrons also have a wave nature. Using this pattern and Bragg's equation they were able to calculate the electron's wavelength, and this corresponded to that predicted by de Broglie's equation \(\lambda = \frac{h}{mv}\). Thus, D&G's experiment provided support for de Broglie's hypothesis and led to the new matter-wave theory. I definitely think this question should be worth more than 2 marks haha - hope this helps!

So would you talk about how it is an exception to the flowchart as de Broglie did not test the hypothesis himself?
And thank you!

[kiwiberry]

So would you talk about how it is an exception to the flowchart as de Broglie did not test the hypothesis himself?
And thank you!

Hm, I don't think it would be an exception, the flowchart was still followed even though his hypothesis was tested by different people