important experiments paper 1 and 2 Flashcards
Stopping voltage setup
Set up a circuit with a variable supply, ammeter, resistor, and two separate metal plates under incident EM radiation.
Capacitor circuit
Parallel circuit with a switch across the two loops. Cell and capacitor in one loop, resistor and (same) capacitor in the second.
Explain the stopping voltage experiment
Photons arriving at the metal plate cause photoelectrons to be emitted (if above threshold frequency) and cross to the second metal plate. As the voltage of the supply is decreased, it reduces the potential over the two plates. The photoelectrons must do work to overcome this. The voltage at which the photoelectrons can no longer reach the other plate and turn around is the stopping voltage.
Stopping potential
The stopping potential is defined as the potential necessary to stop any electron (or, in other words, to stop even the electron with the most kinetic energy) from reaching the other side.
What does the stopping voltage tell you
eV = 1/2mv^2. You can work out the work function from this (W = QV).
Verifying Coulomb’s law
Charge insulating rods and measure their charge using a Coulomb meter. Place one rod on the top tap balance and zero the scale. Bring the second rod close to the first and measure the change in mass. Repeat, changing either radius of the rod or charges.
Finding the internal resistance of a power supply
Measure the terminal PD, vary the current by changing the load resistance. Plot V against I, the gradient is internal resistance, the y-intercept is the EMF.
Finding the resistivity
Measure the diameter of the wire. Measure the voltage and current for various lengths of the same wire. Calculate the resistances. Plot resistance against length, the gradient is resistivity/area.
Boyle’s law experiment
Slowly use the foot pump to increase the pressure. Record the volume for different pressure levels. Plot P against 1/V, if the graph is directly proportional, it follows Boyle’s law.
Charles law experiment
Record the volume and temperature of the cold water. Heat the water and record the temperatures. Plot volume against temperature. If the graph is a straight line and approximately crosses the x-axis at -273 degrees, it follows Charles law.
Gay-Lussac’s experiment
Heat is applied to the cylinder. Measure the temperature and volume at regular intervals. Plot P against T, if it’s a straight-line graph, then it obeys the law.
How do Gay-Lussac’s and Charles’ experiments give evidence for absolute zero temperature?
They should be directly proportional; however, they are not, and both intersect the x-axis at -273. This gives evidence for the Kelvin temperature scale, where 0K is absolute zero.
Rutherford’s scattering experiment
A stream of alpha particles from a radioactive source were fired at a very thin gold foil sheet. The number of alpha particles at different angles was recorded.
Rutherford’s scattering experiment conclusions
Most (fast-charged) alpha particles went straight through, therefore an atom is mostly empty space. Some alpha particles deflected at an angle greater than 90°, therefore part of the atom must be more massive than the alpha particle; this is the nucleus. Alpha particles were repelled, therefore the nucleus must be positively charged. Since atoms are neutral overall, electrons must be in the outside of the atom.
Trigonometric parallax
The star is viewed from two positions at 6-month intervals. The change in angular position of the star against the background of fixed stars is measured. Trigonometry is used to calculate the distance to the star. The diameter/radius of the Earth’s orbit about the Sun must be known.
