Author Topic: SUGGESTED SOLUTIONS (Read 22930 times)

GeniDoi · « **Reply #30 on:** November 11, 2015, 10:54:21 pm »

It's a photo diode as an LDR isn't a transducer but rather just a resistor. A photo diode actually produces a time-varying electrical current from the light energy that is incident upon it, which the amplifier boosts up. I think the amplifier is the key here

odeaa · « **Reply #31 on:** November 11, 2015, 10:58:14 pm »

Quote from: GeniDoi on November 11, 2015, 10:54:21 pm

It's a photo diode as an LDR isn't a transducer but rather just a resistor. A photo diode actually produces a time-varying electrical current from the light energy that is incident upon it, which the amplifier boosts up. I think the amplifier is the key here

Phew

jyce · « **Reply #32 on:** November 11, 2015, 10:59:03 pm »

I'm fairly confident an LDR is also a transducer. When the intensity of light on it changes, its resistance changes and so current changes.

GeniDoi · « **Reply #33 on:** November 11, 2015, 11:06:54 pm »

Quote from: jyce on November 11, 2015, 10:59:03 pm

I'm fairly confident an LDR is also a transducer. When the intensity of light on it changes, its resistance changes and so current changes.

The LDR wastes energy by converting some to heat based on light intensity and this produces a time varying voltage. For this to work, there needs to be a power supply to supply power for it to waste. You can't have a resistor connected to an unpowered circut - it won't produce a time varying voltage because there is no voltage for it to alter, by the definition of an unpowered circut.

There is no indication in the diagram that a power supply exists in the demodulating circuit. Moreover, an amplifier in such a circut would be illogical at best as the power supply should be supplying all of the power to the loudspeaker for it to function. The only way that it makes sense is if a photo diode is producing a very small time varying current which the amplifier amplifies.

Occam's razor...

jyce · « **Reply #34 on:** November 11, 2015, 11:10:24 pm »

Quote from: GeniDoi on November 11, 2015, 11:06:54 pm

The LDR wastes energy by converting some to heat based on light intensity and this produces a time varying voltage. For this to work, there needs to be a power supply to supply power for it to waste. You can't have a resistor connected to an unpowered circut - it won't produce a time varying voltage because there is no voltage for it to alter, by the definition of an unpowered circut.

There is no indication in the diagram that a power supply exists in the demodulating circuit. Moreover, an amplifier in such a circut would be illogical at best as the power supply should be supplying all of the power to the loudspeaker for it to function. The only way that it makes sense is if a photo diode is producing a very small time varying current which the amplifier amplifiers.

Occam's razor...

Sure. I'll change it.

dankfrank420 · « **Reply #35 on:** November 11, 2015, 11:12:46 pm »

Re: 17b

Shouldn't the answer be C?

More diffraction, and since the ratio of lamba/s must be greater then s must be a smaller number?

Also I got the same answer for the last question 7.3*10^7

Davos · « **Reply #36 on:** November 11, 2015, 11:13:14 pm »

Quote from: dankfrank420 on November 11, 2015, 11:12:46 pm

Re: 17b

Shouldn't the answer be C?

More diffraction, and since the ratio of lamba/s must be greater then s must be a smaller number?

Also I got the same answer for the last question 7.3*10^7

agreed

yeahm8 · « **Reply #37 on:** November 11, 2015, 11:13:54 pm »

20b. What evidence do we have that electrons behave like waves...

jyce · « **Reply #38 on:** November 11, 2015, 11:15:24 pm »

Quote from: yeahm8 on November 11, 2015, 11:13:54 pm

20b. What evidence do we have that electrons behave like waves...

Ugh. Okay I'll fix that.

GeniDoi · « **Reply #39 on:** November 11, 2015, 11:17:32 pm »

Quote from: jyce on November 11, 2015, 11:15:24 pm

Ugh. Okay I'll fix that. Surely that's a repeat of Question 21a?

I'm pretty sure for 21a you could also alternatively mention a modified double slit experiment firing electrons rather than photons since electrons fired through the two slits produce an interference pattern that is a property of waves.

yeahm8 · « **Reply #40 on:** November 11, 2015, 11:17:47 pm »

Quote from: jyce on November 11, 2015, 11:15:24 pm

Ugh. Okay I'll fix that.

yep pretty much, also there was a multitude of things we could have spoken about for 20a correct? not just photoelectric effect?

jyce · « **Reply #41 on:** November 11, 2015, 11:20:29 pm »

Quote from: yeahm8 on November 11, 2015, 11:17:47 pm

yep pretty much, also there was a multitude of things we could have spoken about for 20a correct? not just photoelectric effect?

True, although the photoelectric effect is really the only piece of evidence within the VCE Physics course.

jyce · « **Reply #42 on:** November 11, 2015, 11:20:54 pm »

Quote from: GeniDoi on November 11, 2015, 11:17:32 pm

I'm pretty sure for 21a you could also alternatively mention a modified double slit experiment firing electrons rather than photons since electrons fired through the two slits produce an interference pattern that is a property of waves.

Yes, but this is not on the study design.

GeniDoi · « **Reply #43 on:** November 11, 2015, 11:24:57 pm »

Quote from: jyce on November 11, 2015, 11:20:54 pm

Yes, but this is not on the study design.

But you could have used it and still gotten marks?

jyce · « **Reply #44 on:** November 11, 2015, 11:25:41 pm »

Quote from: GeniDoi on November 11, 2015, 11:24:57 pm

But you could have used it and still gotten marks?

Yes, but I'm not going to put it in the suggested solutions is all.

I think you meant question 20a, and not 21a by the way.

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