# Physics Practical Summaries

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

Please use the four separate pages for Core and Advanced Physics instead.

# 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

# Advanced Physics I

**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)