# Physics Practical Summaries

This is old - I made these notes so I could prepare for the mock.

# Core Physics I

## CP 1 Determining the acceleration of a freely falling object:

• Drop a flat object through two light gates. Vary the distance between them
• Plot distance against time squared. Multiply the gradient by 2 to get the acceleration due to gravity

## CP 2 Determining the resistivity of a wire:

• Measure the diameter in several places with a micrometer and find the mean
• Measure the current and pd for several different lengths
• Plot resistance against length (should be through origin)
• Multiply the gradient by the cross sectional area ($A = \pi r^2$$A = \pi r^2$) to get the resistivity

## CP 3 Finding internal resistance and emf:

• Connect a fixed resistor and a cell (or a potato). Add an ammeter in series and voltmeter in parallel
• Take readings with different resistors
• Plot pd against current. It should have a negative gradient
• The $y$$y$-intercept is the emf
• The negative of the gradient is the internal resistance

# Core Physics II

## CP 4 Finding the viscosity of a liquid:

• Drop a ball of known diameter into a cylinder of liquid. Measure the time it takes to fall a marked distance
• Stokes' law ($F = 6\,\pi\,\eta\,r\,v$$F = 6\,\pi\,\eta\,r\,v$) can now be used to calculate the viscosity of the liquid
• Multiple balls of different diameters could be used to improve the results as there will be a large uncertainty in time measurements

## CP 5 Finding the Young modulus of a material:

• Clamp a long copper wire inside some wooden blocks. The other end should go over a pulley attached to a mass
• Measure its diameter in several places and calculate the mean
• Attack a paper marker to the wire, over a ruler
• Record the distance between the marker and clamped end. This is $l$$l$
• Increase the weight and record the mass and difference between the base length and current one
• Calculate stress and strain
• Plot a stress-strain graph through the origin
• The Young Modulus is the gradient

## CP 6 Calculating the speed of sound in air:

• Connect a microphone and signal generator to an oscilloscope as inputs
• Connect a speaker to the same signal generator
• Move the microphone until the waves are in phase. Record this distance. Keep doing this, moving the microphone further away
• Find the mean of the distances between each pair of readings. Multiply this by the frequency (from the signal generator, or the oscilloscope for greater accuracy)

## CP 7 The effects of length/tension/mass per unit length on a vibrating string:

• Use a signal generator and vibration generator to vibrate a string connected to a mass through a pulley
• You can modify the length, tension or mass per unit length. Then adjust the frequency until one wavelength of a standing wave is formed
• Plot a graph of $\frac{1}{f}$$\frac{1}{f}$ against $\lambda$$\lambda$. The gradient is the mass per unit length
• Use the equation $f = \frac{1}{2l} \times \sqrt{\frac{T}{\mu}}$$f = \frac{1}{2l} \times \sqrt{\frac{T}{\mu}}$

## CP 8 Using a diffraction grating to calculate the wavelength of a laser:

• Put a diffraction grating over a laser. Clamp this a set distance from a wall
• Measure the distance between the zero order (centre) and first order dots (each side of the central one). Take the mean between these two readings
• $\theta = tan^{-1}($$\theta = tan^{-1}($distance between dots $\div$$\div$ distance from laser to wall$)$$)$
• $\lambda =$$\lambda =$ distance from laser to wall $\times sin\,\theta$$\times sin\,\theta$

## CP 9 Proving $\Delta p = F\Delta t$$\Delta p = F\Delta t$:

• Create a surface for a trolley. Compensate for friction. (or use an air track)
• Set up two light gates. Connect the trolley to a hanging mass with a pulley and string. $m_{\mathrm{system}} =$$m_{\mathrm{system}} =$ trolley mass $+$$+$ hanging mass
• Release the trolley from the top. Use the change in velocity from the light gates in $\Delta p_{\mathrm{system}} = m_{\mathrm{system}} \Delta v$$\Delta p_{\mathrm{system}} = m_{\mathrm{system}} \Delta v$
• Divide this by the time between the two light gates ($\Delta t$$\Delta t$)
• Calculate total force with $F = Mg$$F = Mg$ ($M$$M$ is the hanging mass)
• Do repeats, and vary the hanging mass
• Plot $F$$F$ against $\Delta p_{\mathrm{system}}$$\Delta p_{\mathrm{system}}$
• If it's a straight line, $\Delta p = F\Delta t$$\Delta p = F\Delta t$

## CP 10 Analysing collisions between small spheres:

• Roll a sphere into another, whilst recording with a video camera. Put rulers on the table in view of the camera
• Use software to find the distance travelled each frame, in $x$$x$ and in $y$$y$. Multiply each by the framerate to get the velocity in that direction
• The total momentum before and after the collision should be equal

## CP 11 Analysing capacitor charging and discharging:

• Connect a CRO to a capacitor-resistor circuit (in parallel)
• Set the timebase to 0 so there's a dot rather than a wave
• Use a timer (with lap function) to record the time it takes to fall/rise one division for an entire charge/discharge
• Plot a V-t graph
• (or use a data logger, ammeter and voltmeter)