Basics of the IB SL Physics

Ch8. Outline, with reference to energy changes, the operation of a pumped storage hydroelectric system. [2]

- friction losses in walls of pipe; - thermal energy losses / in electrical resistance of components; - water requires kinetic energy to leave system so not all can be transferred.

Ch2. The girl chooses to jump so that she lands on lonely-packed snow rather than frozen ice. Outline why she chooses to land on the snow. [3]

- loosely packed snow has large deformation than frozen ice, - so that there is longer contact time. - As change of momentum is the same, longer contact time leads to less reaction force by F=∆p/∆t, - so the girl could land softly on the snow.

Ch7. Rutherford constructed a model of the atom based on the results of the alpha particle scattering experiment. Describe the model. [2]

- most of the mass of the atom is confined at the very small nucleus; - all the positive charge is confined within a very small nucleus; - electron orbit the nucleus in circular orbits.

Ch8. Suggest how the difference between λsun and λearth helps to account for the greenhouse effect. [3]

- wavelength of radiation from Sun is shorter than that emitted from Earth, and is not absorbed by the atmosphere; - infrared radiation emitted from Earth is absorbed by greenhouse gases in the atmosphere; - this radiation is re-emitted in all directions including back to Earth.

Ch6. The copper wires and insulator are both exposed to an electric field. Discuss, with reference to charge carriers, why there is a significant electric current only in the copper wires. [3]

- when an electric field is applied to any material, it acts to accelerate any free electrons; - copper wires have many delocalized electrons as the charge carriers to conduct electric current, - whereas insulators have no charge carriers

Ch7. Rutherford and Royds identified the helium gas in cylinder B by observing its emission spectrum. Outline, with reference to atomic energy levels, how an emission spectrum is formed. [3]

- when electron drops from high energy state to low state, it emits discrete energy, - corresponding to the difference between the energy levels. - frequency of photon is related to energy change, E = hc/λ, hence is also discrete, - giving discrete line structures of atomic spectra.

Ch3. Outline the difference between the molecular structure of a solid and a liquid. [1]

In solid state, molecules have strong forces of attraction. In liquid, there is sufficient energy to break and reform inter-molecular bonds.

Ch6. Define Ohm's law [1]

The current through an ohmic conductor is directly proportional to the p.d. across it when temperature is constant.

Ch6. State what is meant by the emf of a cell. [2]

The work done per unit charge made available by a source in moving charge from one terminal of cell to the other.

Ch5. State what is meant by the principle of superposition of waves. [2]

When two waves coincide, the displacement of each wave add vectorially to give the resultant displacement.

Ch7. The wall of cylinder A is made from glass. Outline why this glass wall had to be very thin. [1]

alpha particles highly ionizing/ alpha particles have a low penetration power/ thin glass increases probability of alpha crossing glass

Ch6. Explain, in terms of electrons, what happens to the resistance of the cable as the temperature of the cable increases. [3]

- As temperature increases, there is greater vibration of metal ions, with increased collisions of electrons. - Drift velocity decreases so current increases. Since V is constant, R will increase.

Ch7. Distinguish between hadrons and leptons. [3]

- Hadrons experience strong force while leptons do not experience strong force. - Hadrons are made of quarks while leptons are fundamental without quarks.

Ch3. Explain, in terms of molecular motion, the change in pressure when volume is increased under constant temperature. [2]

- When average KE remains unchanged, if volume of gas expands, gas molecules will spread out and the frequency of collisions with the inner wall of container will decrease. - There is less rate of change of momentum, so the pressure decreases by P=F/A.

Ch5. One of the slits is now covered. Describe the appearance of the pattern on the screen. [2]

- The intensity of the central maximum is the brightest. - There are subsidiary maxima on either side, with intensity decreases when angle increases. - The width of the central fringe is twice of the width of subsidiary maxima.