Core Practicals Flashcards
Core practical 1
Determine the acceleration of free fall of a small object
Method for determining acceleration of a free falling object? (CP1)
- set up a circuit with a switch, trapdoor, timer, electromagnet with a ball bearing attached to it
- measure height from bottom of ball to the trap door
- flip the switch (flip flip)
- the ball falls to the trap door which breaks the circuit and stops the timer
- repeat 3 tines and average from that height then use different heights
- find g from graph of displacement vs time^2
What equipment can be used to give a more accurate figure for g? (CP1)
- using a small heavy ball so there’s no air resistance
- having a computer automatically release and time the fall gives smaller uncertainty
- make h larger so there’s a smaller percentage uncertainty in the measurement
Core practical 2
Determine the resistivity of a material
Method for resistivity of a material to be found. (CP2)
1) use a micrometer to measure diameter of wire in 3 different places
2) use diameter to calculate cross sectional area
3) the test wire should be clamped to a ruler and connected to a circuit using crocodile clips
4) record the length of wire connected in the circuit, the voltmeter readings and ammeter readings
5) use V=IR to calculate resistance for each length
6) plot graph of resistance x area vs length
7) gradient is resistivity
What could affect the resistivity of the material and how can it be limited? (CP2)
Temp can alter resistivity so use a small current to prevent the wire heating up and changing figures.
Turn circuit off between measurements
Graph for CPAC 1 acceleration of free falling object
Y = displacement X = time^2 G = 1/2 acceleration
Equation
S = ut + 1/2at^2
Graph for CPAC 2 determine resistivity of a material
Y = resistance x area X = length of wire Gradient= resistivity
Equation
resistivity = RA/l
CPAC 3
Determine the emf and internal resistance of an unknown power supply
Method for CPAC 3 finding the emf and internal resistance of a power source
1) set up a circuit with a power supply, an ammeter and variable resistor with a voltmeter in parallel to it
2) vary the resistance and measure current and voltage
3) plot a graph of V against I
4) gradient = negative internal resistance, Y intercept = emf
Graph for CPAC 3 finding the emf and internal resistance of an unknown power supply
Y = voltage
X = current
G = negative internal resistance
Y intercept = emf
Equation
V= emf -Ir
CPAC 4
Determine the viscosity of an unknown liquid
Method CPAC 4 determine the viscosity of an unknown liquid
1) weigh balls, measure radius and work out their density
2) place 3 rubberbands around the tube and time each time the ball passes a band
3) measure distance between bands and calculate velocity
4) plot graph of v against r^2
5) gives gradient of 2g x (Ps-Pl)/9n
Graph for CPAC 4 viscosity of liquid
Y = velocity X= radius^2 G= 2g x (Ps-Pl)/9n
Equation
n = 2r^2 x g x (Ps - Pl)/9v
CPAC 5
Determine the Young’s modulus of a material