experiment info to prepare for unit 3

8/18/2019 Experiment Info to Prepare for Unit 3

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Experiment: finding the resistivity of copper

Diagram:

List of apparatus:

● 1 meter length of copper

● Leads

● Crocodile heads

● Ammeter

● Voltmeter

● Power supply● Variable resistor

Quantities measured:

● Voltage across the wire

● The current flowing through the wire

● The length of the wire

● The area of the wire by finding the radius of the wire by using a micrometer

The independent variable is the length of the wire.The dependant variable is resistance across the wire.

Graph:


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The equation used is

The result is calculated by drawing the line of best fit for the graph above. You

then find the gradient of the line. Finally, to find the value of the resistivity of

copper, you multiply the gradient by the area of the wire.

There is an uncertainty with the micrometer as the micrometer has an uncertainty

with the equipment, which is said to be a systematic error, which is about plus or

minus 0.01 mm.

Lastly, there is uncertainty with that when the current is flowing through the wire,

the copper wire heats up which will increase the resistance of the wire due to

collisions with the lattice ions of the metal and the flowing electrons.

Safety:

Wear goggles to protect your eye and wear a lab coat.

Don’t touch the wires and plug with wet hands


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loading/unloading

List of apparatus

Diameter of wire

Initial length of wire

Length of wire after each added weight

Equal differences between each weight and the following one

Extension of the wire after each added weight

Quantities measured

Weights

Length of wire

equation

Young modulus = stress

Strain

Safety

Wear safety goggles

Tie hair back

Make sure nothing is placed under the weights

Uncertainty

mm


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5/29

Photoelectric Effect

Diagram:

Apparatus:

UV lamp

Negatively charged plate- charged by polythene rod

Power supply- connected to UV lamp source and the charged plate


Nothing really. We just get the results table, as we can’t find the kinetic energy and frequencywith the equipment we have.

I/D Variables:

Independent: Frequency (of light)

Dependent: Kinetic energy (of electron)

Graph Drawn:


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Equation Used:

Total Energy= Kinetic energy + (work function*Planck’s constant)

Result Calculated:

Gradient= Planck’s constant

Work function= -y intercept

Threshold Frequency= x intercept

Uncertainty:

A lot, since we’re dealing with electrons which have very little energy (but we can’t actually

calculate the uncertainty)

Safety:

Safety glasses which filter out UV light, as UV radiation is harmful


7/29

OHM’S LAW

Diagram:

List of Apparatus:

Ammeter, Voltmeter, Wire, Power supply, Leads, Crocodile clips, Rheostat.

Quantities Measured:

Potential difference across wire, Current through wire.

I/D variables:Independent: Voltage

Dependent: Current

Graph Drawn:


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Equation Used:

R=V/I

Result Calculated:

Resistance is constant which shows that current is proportional to voltage. This

proportionality is Ohm’s Law.

Uncertainty:

Voltmeters and Ammeters are only accurate to 0.01. The wire in the circuit used

also increases in temperature as current increases.

Safety:

Do not touch naked wire, Do not use high voltages


9/29

Finding Young’s Modulus

Apparatus:

● Ruler

● Copper Wire

● Pulley

● Weight

● G-Clamp

● Tape

● Wooden Blocks


1. Measure the length of the wire

2. Measure how far the tape moved from the initial position

3. Calculate the extension: Initial Length- Final Length

Independent Variable Dependent Variable

Weights Extension of the wire


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Equation Used:


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Uncertainty:

● To minimise errors the control wire is the same length, diameter and material as

the test wire. This means that errors due to expansion during the experiment

are avoided as the test wire and control wire would both expand by the sameamount and the scale would adjust position and eliminate the error.

● The wire must have no kinks in it otherwise there will be big extensions due to

the wire straightening out rather than just stretching.

● Care must be taken that the limit of proportionality is not exceeded . This can

be checked by removing the load after each addition of the weight. If the limit has

not been exceeded the wire should return to the length it was before the weight

was added.

● The wire is as long as possible (usually about 2m long) and it is as thin as

possible so that as big an extension as possible

can be recorded. (A typicalextension for a 5N loading will be 1mm).

Safety:

● Heavy weights can cause problems if dropped on someone's toe. Care must be

taken not to stand so that the masses are over your foot!

● The wire is very thin and taut. It is possible to cut yourself on it if you walk into it.

The area you are working in should be 'fenced off' so that someone doesn't hurt

themselves.

● The wire might snap. If it does it might whip into your face and eyes. Goggles

should be worn and the area around the wire should be clear so that if you have

to move out of the way you can do so quickly.


12/29

I-V Graphs

Diagrams:

Filament Lamp

Diode

Ohmic Conductor

See Shady

Apparatus:

Filament Lamp:

Power supply

Wires

Ammeter

Voltmeter

Variable Resistor

Filament Bulb

Diode:

Power supply

Wires

Ammeter

Voltmeter

Variable Resistor

Diode

Resistor


FOR BOTH: Potential difference across Filament Bulb/Diode and Current.


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I/D Variables:

FOR BOTH:

The Voltage is the independent variable

The Current is the dependant variable

Graph Drawn:

Filament Bulb: Diode:

Equation Used:

R=V/I

Result Calculated:

Find the Gradient and Invert the answer as V is the x-axis and I is the y-axis

Uncertainty:

Voltmeters and Ammeters are only accurate to 0.01 V/ 0.01 A respectively. Wires

heat up and may lead to an inaccurate results.

Safety:

Do not touch naked wire and avoid using high voltages.


14/29

Experiment: Finding gravitational acceleration (g)

Diagram:

Apparatus:

● Ball

● Meter rule● Camera (that can give you time)


● The distance travelled by the ball (the distance it was dropped from)

● The time it took for the ball to reach the ground

The independant variable is distance the ball is dropped from the ground.

The dependant variable is the time it took for the ball to reach the ground.


15/29

The graph drawn, equation used, how to calculate resultant:

Uncertainty and safety:

● Ball may be released between 1st and 2nd images (so times used all toolong because they include a short time before it is dropped)

● ball released before the 1st image so u is not 0

● the ruler is not vertical/straight the idea that the camera has not been

calibrated correctly i.e. runs too fast/slow

● the idea that there is a parallax error from camera to object

● Put on goggles and lab coat


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MS for a unit 1 exam:

state sufficient quantities to be measured (e.g. s and t OR v, u and t OR u, v and

s)) (1) relevant apparatus (includes ruler and timer/data logger/ light gates) (1)

describe how a distance is measured (1) describe how a speed or time is

measured (1) further detail of measurement of speed or time (1) vary for

described quantities and plot appropriate graph (1) state how result calculated (1)

repeat and mean (one mark max for any relevant quantity/result) (1)


17/29

Refractive Index Experiment

Diagram:

Apparatus:

Ray box

Protractor

Pencil + Ruler


Angle of incidence

Angle of refraction

- Repeat over different angles of incidence

- Work in a dark room

- Make a thin ray

I/D Measured:

Independent: Angle of Incidence

Dependent: Angle of refraction

Graph Drawn:

sini on y-axis

sinr on x-axis


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Equation Used:

sini/sinr = n

Result Calculated:

gradient= refractive index of material

Uncertainty:

+- 1 degree: uncertainty of protractor

Safety:

Safety goggles

Shoes


19/29

Resistivity of a Metal Wire

Diagram

Apparatus

Voltmeter

Ammeter

Resistance wire

Micrometer

Crocodile clipMetre rule

Quantities Measured

Diameter of the Resistance Wire (then calculate cross-sectional area)

Voltage and Current at each length - Resistance is calculated using V/I

Length of the Resistance Wire

Independent Variable - Length of the resistance wire

Dependent Variable - Resistance (Voltage/Current)

Graph Drawn -


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Y-axis: Resistance/ohms

X-axis: Length/metres

Equation

R, the gradient of the graph= p(resistivity), when the equation pl = R is

L area A

rearranged.

Safety:

Make sure your hands are not wet when you are doing the experiment to

avoid an electric shock. You will die otherwise. Keep all switches off when

they are not needed - Emily.


21/29

Hooke’s law

Force = spring constant x extension (F=KX)The spring constant k is measured in

Nm -1 because it is the force per unit

extension

Hooke's Law states that, for

certain elastic materials, force

is proportional to extension

limit of proportionality: is the is

the point beyond which Hooke's

law is no longer true when

stretching a material.

elastic limit: is the point beyond

which the material you are stretching becomes permanently stretched so that the

material does not return to its original length when the force is removed.

Yield point : after this point there is large extension for little stress

The apparatus:● Spring

● Ruler

● Clamp● Different weights

This experiment is set up as shown in the

diagram and the extension recorded down

for each mass, which you can then find out the spring constant by using the


22/29

equation F=KX. a graph can then be plotted to show the elastic limit, the

limit of proportionality and yield point.


23/29

Experiment: Terminal velocity of a sphere

Diagram:

List of apparatus:

● Long measuring cylinder

● Metal sphere

● Markers/Light gates

● Ruler

● Timer

● Micrometer

Quantities measured:● Diameter of sphere

● Distance travelled

● Time taken

Independent variable : Diameter

Dependant variable : Velocity

Graph drawn:

● Calculate radius from diameter

● Calculate velocity from distance and time

● Plot a graph of v/r 2

● Gradient = 9n2(ρ s−ρ f ) g


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Equation used :

Uncertainty:

● Terminal velocity is not reached

● Reaction time● Temperature not constant

● Measurement of diameter

● Micrometer zero error

● Measurement of distance fallen

● Parallax error

Safety:

● Mop up spills

● Wear goggles to avoid splashes in eyes

● Use gloves● Normal lab rules

● Low risk equipment


25/29

Series and Parallel Circuits

Unit 3

Diagrams:

Series Circuit:

Parallel Circuit:


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Apparatus:

● Wires

● Resistors

● Voltmeter● Ameter

● Power Supply


Voltage and Current in both series and parallel circuits.

I/D variables:

● Current is dependent in both.

● Voltage is independent in both.

Uncertainty:

+/- 0.01 Volts or Amps

Safety:

● The voltage of the electricity and the available electrical current can cause

electrocution.

● Don’t touch electricity with wet hands.

● Keep the power supply on a low voltage so the wires don’t heat up.


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Graphs:


28/29

Emf and Internal resistance

Diagram:

List of apparatus:

Dry cell

d.c. Voltmeter (0-5 V)

d.c. Ammeter (0 –1 A)

Switch

Rheostat

Connecting wire


In this experiment, we will measure the e.m.f. and the internal resistance of a dry cell. In order to

investigate the objective of the experiment, we should connect the apparatus as the above electric

diagram. The voltmeter should be connected in parallel circuit while the ammeter should be

connected in series circuit, otherwise, it may cause the inaccurate reading of the meters. Besides, we

investigate the terminal potential difference V varies with the current I, hence we find out the internal

resistance and the e.m.f by plotting the voltage – current graph. By vary the resistance of the

rheostat R, the current I also varies. The terminal potential difference V across the dry cell is given

.by V = – Ir

:I/D Variables

Independent: Voltage

Dependent: Current


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:Graph

Equation used:

.V = – Ir

Safety:

Secondly, the rheostat should be set to its maximum value in the beginning of the experiment, so that

the current is the lowest at first, then increase gradually. As high current produces heat, it would

increase the resistance of the connecting wires and the internal resistance. The current through the

wire will heat up the wire and lead to increase resistance of the apparatus. It may lead to the

inaccurate and imprecise data obtained and hence the inaccurate calculated value of the e.m.f and

internal resistance in the dry cell. Therefore, we should not leave the circuit connected longer than

.necessary to take the readings

In addition, we should ensure the ammeter and voltmeter are connected to the cell with suitable way

(positive terminal to the direction of positive terminal and negative terminal to the direction of

negative terminal). Hence the ways of connection of ammeter and voltmeter also should be in correct

ways (voltmeter in parallel while ammeter in series). Otherwise, the pointer will deflect to the

opposite direction. The ammeter and voltmeter may be damaged

experiment info to prepare for unit 3

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