photoelectric effect/ 2013 physics isa

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  • Created by: bambi
  • Created on: 26-03-13 15:18
what is excitation
the electrons are raised from their orbital into another subshell
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how are electrons excited
through uv radiation (photons)
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how is light emmitted
the electrons deexcite making the electron return to its ground state and this emits a photon of light
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what is ground state
the lowest energy state an electron can be in
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Define photo electric effect
when a photon strikes a metal surface and if it meets the threshold frequency than an electron is emitted from the surface of the metal
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what is the work function
the miniumum energy required to remove an electron from the surface of a metal
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photoelectric effect equation
maxEk=hf- thresold frequency maximum kinetic energy= placks constant x frequency- work function
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what is y=mx+c for e=hf - threshold frequency in terms of a graph?
y axis = maximum kinetic energy , gradient equals placks constant, x axis is frequency and the negative work function is the y intercept
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threshold frequency equation
work function= hfo fo equals threshold frequency h is placks constant
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what is threshold frequency
the lowest frequency of electromagntic radiation/photons that will result in the emission of photoelectrons
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what is a fair test
a fair test is a test which the iv is allowed to affect the dv. this means only changing the iv and controlling the other factors and variables to keep the same
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How can you ensure validity? why?
by keeping a fair test to be able to draw a valid conclusion from the results
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name three factors that cant be controlled
1 humidity/drafts 2 air movements 3 temperature changes in the room
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why do you think you could be instructed to switch off or disconnect the cell between readings?
to prevent the cell overheating or running down
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to what sig fig do you place the percentage uncertainty?
2 sig figures
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how do you rearrange Y=Mx+c for the ISA
y=C+Mx
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how do you work out the gradient of the graph
y axis/X axis
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how do you calculate the percentage uncertainty
precision/ reading * 100
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state the precision of the instrument used
+ or minus 0.01 A/V
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What is the difference between a systematic and a random error
SYSTEMATIC part of the experiment, predictable, occurs each time you measure.RANDOM external source causes problems, no way of predicting, will only occur sometimes.
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if a resistor R came into contact with the connecting clips or plugs , how would that effect the values of current I ?
The current would fall
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what is meant by the term precision?
how small a measurement is
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What is a continous variable ?what type of graph should be used for this type of data?
a variable that can have any numerical value. A line graph should be used to represent this data.
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how can you make your results more reliable?
repeating the experiment and getting the same results
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state the list of 8 things that you must remember?
1 iv/dv 2 equipment ( diagram) 3 no of readings (min 7) 4 repeats 5 show of findings ( graph average) 6 linear/ directly proportional 7 reduce uncertainty ( disconnect the cell after each reading) 8 safety
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how does changing the temperature 10'c effect the percentage of the resistance of the wire
every 10'c changes 5%
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what is meant by the term relability
repeatable results that will follow the general pattern.also when repeated , the results will be the same or similar
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what does y= mx+ c represent
the equation of a straight line
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when assessing the reliability of your experiment, what do you talk about?
either the spread of repeats, or the closeness to the line of best fit
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how do you calculate the percentage uncertainty in your largest mean current reading?
uncertainty= half the range / mean (+ or - 0.5) * spread of results
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state and explain the type of error introduced by contact resistance?
systematic error because it is a fault within the equipment. Everytime contact is made, the resistance is the same
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Name 2 ways of identifying if results are unreliable ?
the repeats widely vary and there is no pattern seen in results
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what is meant by the term accuracy?
how close the results are to the true value
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what is a categoric variable? what type of graph should be used to represent this data?
a variable that is described by a abel. a bar chart should be used to represent this
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why do you need control variables?
to ensure the only factor effecting the dependent is the independant
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what is precision?
the smallest no zero reading that can be measured using an instrument
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what is the precision of a multimeter?
+ or - 0.00001 amps
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what is the presicion of a voltmeter?
+ or - 0.01 volts
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what is the independent variable ?
the variable that is changed
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what does a straight line relationship show ?
the variables are proportional if the line passes through the origin or it is liner if the line does not pass through the origin if you have a curve simply state that they are not proportional because it is a curve
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what is the dependent variable?
The variable that you measure
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how should the range be decided?
a maximum and minimum should be decided that is as large as possible and at least 8 variables should be chosen at equal intervals across the range
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what do you state if the relationship is linear?
that the libne is straight and does not pass through the origin , it is in the form of y=mx+c, c being the y intercept
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what do you state if the relationship is proportional?
that the line is straight and that the line passes through the origin
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how do you find the y intercept ?
extend the line of best fit to cross the x axis . as it can only be found where the upper line touches zero
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What is the constant on the graph with emak against frequency?
Planck's constant - emak= hf - work function
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how do u find the y intercept if neither point starts at zero?
find the gradient , chosse a pont on your line f best fit, use mx+c m is gradient x is the x coordinate . c= the y intercept
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what is a random error?
when repeat readings vary slightly, but not in a predictable way
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how do you reduce the effects of a random error ?
take more repeats to get a more relaible average ; use more accurate equipment. take human error out through electrical timing
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how do you know if you have a low level of random error ?
the results on you graph are closely together : your values are very similar
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what is a systematic error?
one that effects all of the readings taken equally. eg a non zero multimeter , connecting a wire with a high resistance
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how can you tell if you have a systematic error ?
the y intercept will be different from a graph without systematic error as the emf would be higher (gradient is the same)
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how can you prevent systematic errors ?
zero all equipment before starting , check any wire for significant resistance
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what would be the effect of a non zero multimeter and voltmeter when calculating emf and internal resistance?
the emf would be higher the gradient would be the same
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how can you calculate the uncertainty if you only take one reading ?
quote the precision of the instrument eg + or - 0.001 meters for a ruler
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what will the uncertainty be if you take more than one reading and they are the same ?
state the precision of the instrument used
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what is uncertainty if you take more than one reading and they are different?
uncertainty = 0.5 * the range of readings this will be bigger than the precision of the instrument .
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How do u calculate the % uncertainty for one value or values that are the same
the uncertainty/value * 100
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how do you calculate the % uncertainty if more than one value is recorded?
the uncertainty/ the average value * 100
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why do we use percentage uncertainties?
so that you can compare the relative effects of uncertainties in a given experiment
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would a measurement with a high level of accuracy have a high or low % of uncertainty
low - the uncertainty will have less of an effect on the accuracy/ reliability of the result
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how do you keep the percentage uncertainty as low as possible?
make your measurements as large as practically possible . use instruments with a high level of precision
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how do you combine uncertainties when adding or subtracting quantities ?
add absolute uncertainty
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how do you combine uncertainties when multiplying or dividing qauntities
add percentage uncertainties
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how do you combine uncertainties when raising a power ?
multiply percentage uncertainty to the power
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