Paper 1 Model Answers Flashcards
Detecting new atom model through observations of Alpa Rutherford Experiment [4]
[1] Most alpha particles passed straight through undeflected OR some passed through a small angle
[1] A very small number deflected through an angle greater than 90 degrees
[1]This suggests that the alpha particles are deflected by a charged nucleus that has a very small diameter compared to that of the atom rather than the charge being distributed throughout the atom
[1] And most of the mass of the atom is concentrated in the nucleus rather than distributed throughout the atom
Resistance of a thermister changes with temperature [2]
[1] The number of charge carriers increases with temperature (I=nqvA and V=IR)
[1] So this lowers the resistance (despite increased lattice vibrations)
Temperature increase on a metal affecting resistance [3]
[1] A rise in temperature causes the amplitude of the vibrating ions to increase
[1] This causes the number of collisions per second between the ions and the moving electrons to increase
[1] So the rate of flow of electrons decreases (causing the resistance of the metal to increase)
Why electrons follow circular paths in a magnetic field [3]
[1] The magnetic force on the electrons acts at right angles to the plane containing B and v
[1] Hence the force is always towards the centre of the circle
[1] So providing a centripetal force on the electron or a centripetal acceleration that maintains circular motion
Explain how a capacitor discharges [3]
[1] Electrons/charge transferred from the negatively charged plate to positively charge plate through the resistor
[1] Hence the charge on capacitor decreases (exponentially)
[1] Until the charge on the capacitor equals 0/negligible
Terminal velocity explanation of graph [3]
[1] Initial acceleration due to resultant force
[1] Decreasing acceleration as resistive forces increase
Or Decreasing acceleration as resultant force decreases
[1] No acceleration as resultant force is zero
Or constant velocity as resultant force is zero
Terminal velocity: ‘The work done by the cyclist is converted into the kinetic energy of the
cyclist and bicycle.’ criticise [3]
[1] Work done (by cyclist) results in a transfer of energy
[1] initially there is an increase in Ek of (cyclist and bicycle)
Or work done is transferred/converted to other forms of
energy
[1] when the velocity of the cyclist is constant, all the energy is being transferred to other forms
A capacitor is charged when a switch closes describe what happens to the P.d across resistor and capacitor in the circuit [4]
[1] p.d. across capacitor increases Or p.d. across resistor
decreases
[1] p.d. across capacitor increases to 5V
[1] p.d. across resistor starts at 5V and reduces to 0V
[1] Exponentially
Cosmic rays are mainly high‑energy protons which have a
mass less than that of a lambda particle.
Explain why a cosmic ray could lead to the creation of a lambda particle. [2]
[1] Energy of cosmic ray would be turned into matter/mass
[1] According to ΔE = c^2Δm
Explain why neutral particles cannot be directly observed but information about them can be obtained by studying their decay particles. [3]
[1] Neutral particles do not leave a track/ionise
[1] Reference to conservation laws to deduce the properties of particles
[1] Tracks of decay particles can determine the momentum of neutral particle
Explain how P.d varies along a wire [3]
[1] V at top/start = 0V
Or recognition “potential divider”
Or V increases (by implication)
Or V at bottom = 1.5V
[1]Two sections of wire act as series resistors
Or R=el/A
Or comment about R proportional to length
Or V/Vt=R/Rt
[1] potential difference proportional to length of wire
Explain how an electron gun creates a beam of electrons [3]
[1] When the surface of a metal is heated, its free electrons gain thermal energy
[1] When they have enough energy they break free from the surface of the metal [work function]
[1] Once emitted, the electrons can be accelerated using an electric field
