- #31
Osman
- 1
- 0
I think some of u forgot rule 5 in the planning exercise paper, which states:
"Your Plan should be based on the use of STANDARD equipment, apparatus, chemicals and other materials available in a school or college science laboratory."
And the reason being, if ur school's 6th form or ur college doesn't have the equipment in ur plan then ur going to have some problems doing the experiment.
If we go back to the question it's pretty obvious I think:
"You are required to design a laboratory experiment using a light dependent resistor (LDR) to investigate how the intensity of light emitted by a lamp varies with wavelength."
-We have to use an LDR
-We have to investigate the light intensity change with wavelength
This is an OCR paper, and in my OCR physics AS textbook it says in the key notes after the Potential Dividers section:
"Thermistors and light-dependent resistors can be used in potential divider circuits to provide p.d.s that are dependent on temperature and light level respectively."
DING! I think that's a big enough hint to make a Pontential Divider circuit.
For those of you who still don't understand, take out the stuff about thermistors and concentrate on the LDR part:
"LDRs can be used in potential divider circuits to provide p.d.s that are dependent on light level (i.e. intensity of light emitted by a lamp)."
How can they be used? i.e. how is the circuit set-up? LOOK IN UR BOOK! They never test you on something they never taught you.
Your investigation will be based around the potential divider equation:
Vout = Vin * Rb / Ra+Rb
Say Vin (your source voltage) is 12v
Say the fixed resistor (Ra) is 10 ohms
Say the LDR (Rb) exposed to a certain light intensity has a resistance of 1 Ohm (for simplicity).
Vout will then be 12*1 / 10+1 = 12/11 = slightly over 1v output.
Now say the LDR has a resistance of 2 ohms at another light level:
Vout = 12*2 / 10+2 = 24/12 = a 2v output.
Once more, the LDR has a resistance of 3 ohms now:
Vout = 12*3 / 10+3 = 36/13 = almost 3v output.
Now using out knowledge of LDR's: The resistance drops as the light intensity increases.
What our calculations have shown is that a lower resistance of the LDR would result in a lower voltage output. Therefore, as light intensity increases, the voltage output decreases.
part (c) of the planning exercise asks "how a measure of the intensity can be obtained from the LDR" and I think using a potential divider circuit with an LDR answers this.
however, part (b) asks "how the wavelength of the light falling on the LDR is determined". But the question acknowledges it's worked out from a resistance (light falling on an LDR), therefore my best guess is using equations to work out the energy (perhaps W=ItV), and then E=hf => E/h = f to work out the frequency of the light, and finally c = f[lander] => c/f = [lander] (lander is the symbol for wavelength) to determine the wavelength of the light as the question asks.
that's where my discussion ends and I hope u have found this useful
"Your Plan should be based on the use of STANDARD equipment, apparatus, chemicals and other materials available in a school or college science laboratory."
And the reason being, if ur school's 6th form or ur college doesn't have the equipment in ur plan then ur going to have some problems doing the experiment.
If we go back to the question it's pretty obvious I think:
"You are required to design a laboratory experiment using a light dependent resistor (LDR) to investigate how the intensity of light emitted by a lamp varies with wavelength."
-We have to use an LDR
-We have to investigate the light intensity change with wavelength
This is an OCR paper, and in my OCR physics AS textbook it says in the key notes after the Potential Dividers section:
"Thermistors and light-dependent resistors can be used in potential divider circuits to provide p.d.s that are dependent on temperature and light level respectively."
DING! I think that's a big enough hint to make a Pontential Divider circuit.
For those of you who still don't understand, take out the stuff about thermistors and concentrate on the LDR part:
"LDRs can be used in potential divider circuits to provide p.d.s that are dependent on light level (i.e. intensity of light emitted by a lamp)."
How can they be used? i.e. how is the circuit set-up? LOOK IN UR BOOK! They never test you on something they never taught you.
Your investigation will be based around the potential divider equation:
Vout = Vin * Rb / Ra+Rb
Say Vin (your source voltage) is 12v
Say the fixed resistor (Ra) is 10 ohms
Say the LDR (Rb) exposed to a certain light intensity has a resistance of 1 Ohm (for simplicity).
Vout will then be 12*1 / 10+1 = 12/11 = slightly over 1v output.
Now say the LDR has a resistance of 2 ohms at another light level:
Vout = 12*2 / 10+2 = 24/12 = a 2v output.
Once more, the LDR has a resistance of 3 ohms now:
Vout = 12*3 / 10+3 = 36/13 = almost 3v output.
Now using out knowledge of LDR's: The resistance drops as the light intensity increases.
What our calculations have shown is that a lower resistance of the LDR would result in a lower voltage output. Therefore, as light intensity increases, the voltage output decreases.
part (c) of the planning exercise asks "how a measure of the intensity can be obtained from the LDR" and I think using a potential divider circuit with an LDR answers this.
however, part (b) asks "how the wavelength of the light falling on the LDR is determined". But the question acknowledges it's worked out from a resistance (light falling on an LDR), therefore my best guess is using equations to work out the energy (perhaps W=ItV), and then E=hf => E/h = f to work out the frequency of the light, and finally c = f[lander] => c/f = [lander] (lander is the symbol for wavelength) to determine the wavelength of the light as the question asks.
that's where my discussion ends and I hope u have found this useful