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
Method CPAC 5 Young’s modulus of a material
1) clamp a wire, attach a mass to the end over a pulley and add a post it note to the wire
2) measure length and diameter of wire
3) vary the mass on the end of the wire and measure the extension of the wire
4) plot a graph of stress against strain and the gradient is Young’s modulus
Graph for CPAC 5 Young’s modulus of wire
Y = stress X = strain G = Young’s modulus
Equation
Ym = stress/ strain
CPAC 6
Speed of sound
Method for CPAC 6 speed of sound
1) set up a signal generator, oscilloscope, microphone and speaker
2) vary the distance of the microphone to the speaker and record each successive distance where peaks of one trace coincide with the troughs of the other
3) calculate a mean wavelength of the sound and use a trace to determine the frequency
4) multiply wavelength and frequency to give velocity
Graph for CPAC 6 speed of sound
Y = wavelength
X = frequency
Area under graph = velocity
Equation
V = w x f
CPAC 7
Investigate the effects of length, tension and mass per unit length on the frequency of a vibrating string
Method CPAC 7 Investigate the effects of length, tension and mass per unit length on the frequency of a vibrating string
1) attach one end of the string to vibration generator and the other end over a pulley and attach masses to it
2) vary mass to increase tension and measure the length for which a standing wave is formed
3) plot graph of tension against mass per length to give a gradient of velocity^2
Graph CPAC 7 Investigate the effects of length, tension and mass per unit length on the frequency of a vibrating string
Y= T X= U (mass per unit length) G= velocity^2
Equation
V= route(T/U)
CPAC 8
Determine the wavelength of light from a laser or other light source using a diffraction grating
