Practical skills Flashcards
Describe how you would fine the centre of mass of an irregular object
1) Hang the object freely from a point (eg. a corner)
2) Draw a vertical line downwards from the point using a plumb bob
3) Repeat this from a different point of suspension - where the lines cross is the centre of mass
Describe an experiment to demonstrate two-source interference for light
1) Shine a laser through two slits onto a screen - the slits must be of equal wavelength to the laser light so it is diffracted
2) You get a resultant pattern of light and dark fringes
What does Young’s Double Slit experiment demonstrate
Two-source interference for light
Describe an experiment you would use to find a value for g
1) Set up apparatus and measure h, the height between the ball bearing the trapdoor
2) Flick the switch to start the timer and disconnect the EM, releasing the ball bearing
3) The ball bearing will fall onto the trapdoor, knocking it down and breaking the circuit. The timer will then stop - record the time.
4) Repeat for various heights and plot a graph of height against time squared. Gradient of the line of best fit = 1/2g
Describe an experiment you would use to determine the resistivity of a wire
1) Find wire’s cross-sectional area by finding its diameter with a micrometer and then using πr²
2) Clamp the wire to a ruler, with circuit attached the the wire where the ruler reads zero. Then attach flying lead to the test wire
3) Record the length of the test wire and the ammeter and voltmeter readings in the circuit, and use these to calculate resistance
4) Repeat for different lengths and plot a graph of R against L and draw a line of best fit
5) The gradient of the line is equal to ρ/A - multiply the gradient by cross-sectional area to find resistivity
Describe an investigation to find internal resistance and EMF of a circuit
1) Set up a circuit with a battery, ammeter, voltmeter and variable resistor
2) Vary the current by changing the load resistance using variable resistor. Measure the pd for different values of current
3) Plot these results in a graph of V against I
4) V = -rI + ℰ, and since ℰ and r are constants, that is just the equation of a straight line
5) Y-intercept in ℰ and gradient is -r
Describe how you would investigate factors affecting the resonant frequencies of a string
1) Begin by measuring the mass and length of string and then find mass per unit length (kgms-1) from M/L
2) Set up apparatus and work out tension of of string using T=mg
3) Turn on the signal generator and vary the frequency until you find the first harmonic - this is the string’s resonant frequency
4) Then vary the length, tension and mass per unit length to see how these factors vary the frequency
Explain how length, tension and mass per unit length of a string affect its resonant frequency
Increased length lowers resonant frequency as the half wavelength at the resonant frequency is longer
Increased mass per unit length should lower resonant frequency as waves travel slower down the string
Decreased tension will lower resonant frequency as waves travel slower on a looser string
