Unit 5 definitions

Question 1

Internal Energy:

Answer 1

The sum of the random distribution of potential and kinetic energy amongst molecules. In (an ideal) gas the molecules have only kinetic energy and do not have potential energy.

Question 2

Ideal Gas Assumptions:

Answer 2

1. The molecules in the gas can be considered small hard spheres. 2. All collisions between gas molecules are elastic and all motion is frictionless (no energy is lost in collisions or in motion). 3. The gas molecules are constantly moving in random directions with a distribution of speeds. 4. Distance between molecules is much larger (on average) than the diameter of molecules. 5. The time of the collision is much shorter than the time between collisions. 6. There are no forces between the molecules – Internal Energy is all Kinetic (no potential)

Question 3

Absolute Zero:

Answer 3

The temperature at which the atoms of a substance have no thermal/kinetic energy; the lowest possible temperature.

Question 4

Absolute Temperature:

Answer 4

A temperature measured on the Kelvin (or Rankine) scale. Proportional to average translational KE of atoms.

Question 5

Features of Nuclear Decay:

Answer 5

Spontaneous and Random

Question 6

Random:

Answer 6

Cannot identify when an individual nucleus will decay. Can’t know which nucleus will decay next.

Question 7

Spontaneous:

Answer 7

Cannot be influenced by any external factors/ happens without external stimulus.

Question 8

Unstable:

Answer 8

There is an imbalance in the number of neutrons and protons in a nucleus (see N-Z graph).

Question 9

Half-life:

Answer 9

The average time taken for the activity of a sample / the number of remaining unstable nuclei to fall by half

Question 10

S.H.M.:

Answer 10

Required condition is F (or a) =-kx; force (or acceleration) is proportional to the displacement from the equilibrium position and always acting towards the equilibrium position (in the opposite direction

Question 11

Free Oscillation:

Answer 11

Oscillation under no external influence other than the impulse that initiated the motion. Will vibrate at natural frequency.

Question 12

Natural Frequency:

Answer 12

The frequency at which a system oscillates when not subjected to a continuous or repeated external force.

Question 13

Forced Oscillation

Answer 13

Oscillation caused by a driver continually applying a (periodic) force or impulse to the system.

Question 14

June 2010: Discuss how the tuned mass dampers reduce the amplitude of the oscillations of the bridge and explain why they must be very heavily damped.

Answer 14

The springs/dampers absorb energy (from the bridge) (1) (Because) the springs deform/oscillate with natural frequency of the bridge (1) Hence there is an efficient/maximum transfer of energy (1) Springs/dampers must not return energy to bridge / must dissipate the energy (1)

Question 15

Jan 2012: The oscillations of the pan are damped. Explain what is meant by this statement. (2)

Answer 15

Energy of the system is dissipated or energy is removed from the system (by frictional forces) (1) (Hence) the amplitude reduces (1) DO NOT ALLOW ‘LOST’ FOR REMOVED FROM SYSTEM

Question 16

Resonance:

Answer 16

This is when an object is forced to vibrate at a frequency equal/close to its natural frequency Or Driver frequency matches natural frequency of object. There is maximum energy transfer from driver to driven.

Question 17

June 2010:Name the effect that results in a system being driven into large amplitude oscillations, and state the condition necessary for this to happen. (2)

Answer 17

Resonance (1) System driven at / near its natural frequency (1)

Question 18

How damping affects resonance:

Answer 18

An increase in damping will lead to a lower natural frequency with smaller maximum amplitude. Less energy is transferred to the object.

Question 19

Redshift:

Answer 19

The (fractional) increase in wavelength of light received due to the recession of the source from the Earth/observer.

Question 20

Cosmological Red Shift:

Answer 20

: increase in wavelength due to the expansion of the universe (i.e. the space between the galaxies).

Question 21

June 2010: Explain what is meant by the term red shift in this context and state the inference that Hubble made from his measurements.

Answer 21

The observed wavelength is longer than the actual wavelength / the wavelength is stretched out (1) One from: The universe is expanding (1) (All distant) galaxies are moving apart (1) The (recessional) velocity of galaxies is proportional to distance (1) The furthest out galaxies move fastest (1)

Question 22

Standard Candles:

Answer 22

An astronomical object of known luminosity (due to some characteristic property of the object). Typically Cepheid variables and IIA supernovae.

Question 23

June 2013: …. and explain how the use of a standard candle enables the distance to more distant objects to be determined.

Answer 23

Flux/brightness/intensity of standard candle is measured (1) Luminosity of standard candle is known [accept reference to absolute magnitude Or total power output of star] (1) Inverse square law is used (to calculate distance to standard candle) (1)

Question 24

June 2013: Outline how parallax measurements are used to determine the distance to nearby stars….

Answer 24

The star is viewed from two positions at 6 month intervals Or the star is viewed from opposite ends of its orbit diameter about the Sun (1) The (change in) angular position of the star relative to fixed/distant stars is measured (1) The diameter/radius of the Earth’s orbit about the Sun must be known and trigonometry is used (to calculate the distance to the star) [Do not accept Pythagoras] (1) [the marks above may be obtained with the aid of a suitably annotated diagram] e.g

Question 25

How is a H-R Diagram used to find the radii of stars?

Answer 25

How is a H-R Diagram used to find the radii of stars?

Question 26

Nuclear binding energy:

Answer 26

The energy needed to break an atomic nucleus into constituent parts/nucleons Or the energy that is released when a nucleus is assembled from its constituent parts/nucleons. Calculated by finding the mass defect and using E=mc2.

Question 27

June 2013: State and explain the conditions necessary for fusion to occur (3)

Answer 27

Very high temperature to overcome coulomb/electrostatic repulsion (1) so that the nuclei come close enough to fuse/for strong (nuclear) force to act (1) Very high density to maintain a high/sufficient collision rate (1)

Question 28

Nuclear fission:

Answer 28

• A heavy nucleus absorbs a neutron. [accepts “collides with” / “fired into”] • The nucleus becomes unstable and splits into two fragments [accept “decays” / “breaks up” for “splits”] • Idea that a few neutrons are emitted in the fission process • These neutrons cause further fissions Or these neutrons cause a chain reaction (if atom is used instead of nucleus only penalise once) • Energy is released due to the mass difference between the nuclei before and after the fission process (E=mc2). • The daughter products carry this extra energy in the form of kinetic energy (remember KE  T).