physics exam Flashcards
(a) State Newton’s third law of motion.
for every action or force there is an equal and opposite reaction or force
(b) Dublin Port Tunnel is 4.5 km in length and has an 80 km per hour speed limit. Cameras at the entry and exit points are used to determine the average speed of a vehicle driving through the tunnel. What is the minimum time, in minutes, to drive through the tunnel without exceeding 80 km per hour on average?
time = total distance ÷ (average) speed / t = 4.5 / 80 / (t =) 4.5 / 1.3333 / 0.05625 hour → 3.375 minutes
(c) State the principle of conservation of momentum.
- when no external force acts or in a closed system, (total) momentum before (a collision) equals 2. when no external force acts or in a closed system, (total) momentum remains or is 3. when no external force acts or in a closed system, m1u1 + m2u2 = m1v1 + m2v2 or (m1 + m2)v
(d) When struck once with a hammer, a nail of mass 0.018 kg was given a horizontal initial velocity of 8.0 m s–1 and as a result its point penetrated horizontally 0.02 m into a block of wood before coming to rest. Calculate the average force exerted by the wood on the nail.
v² = u² + 2as or 0² = 64 + 2 × a × 0.02 → (a =) (−)1600 m s–2 → (F = ma = 0.018 × 1600 =) 28.8 N
(e) How does Brownian motion provide evidence for the kinetic theory?
shows particles in rapid or random or zig-zag motion / shows particle collisions / shows particulate nature of matter
(f) Explain how sample X of a liquid and sample Y of the same liquid could have the same temperature but contain different quantities of heat.
different mass or different volume
(g) A small gas cylinder of volume 7 × 10–5 m³ contained 0.75 moles of carbon dioxide at a temperature of 293 K. What was the pressure, in Pa, of the gas inside the cylinder?
PV = nRT / P × 7 × 10–5 = 0.75 × 8.31 × 293 → (P =) 2.60 (or 2.61) × 10⁷ Pa
(h) What type of mirror forms an image at infinity of an object placed at its focal point?
concave or converging
(i) Arrange the following forms of electromagnetic radiation in order of increasing wavelength: gamma waves, infrared radiation, x-rays, violet light.
gamma, x-rays, violet light, infrared
(j) What is meant by the diffraction of a wave?
spreading out of a wave or bending of a wave after passing or as it passes an obstacle or through a gap or into geometrical shadow of obstacle
(k) Figure 2 represents a longitudinal wave moving to the right. A = 12 cm. What is the wavelength of the wave?
4 cm
(l) Write an equation to define capacitance.
C = Q/V / (capacitance is) ratio of charge to potential difference
(m) What is a magnetic field?
space or region around a magnet or electromagnet or moving electric charge or current-carrying conductor / where its force acts / where its effects can be detected / where compass needle or iron filings respond
(n) What is the combined resistance of four 9 Ω resistors connected in parallel?
1/R = 1/R₁ + 1/R₂ + 1/R₃ + 1/R₄ / 1/R = 1/9 + 1/9 + 1/9 + 1/9 / 1/R = 4/9 → R = 2.25 Ω
(o) Identify the type of device that changes a 230 V a.c. supply to a 5 V a.c. supply.
transformer
(p) Why are high voltages used to transmit electrical energy over long distances?
economical / less power lost / less heat (lost) / smaller current in wires / wires used can be thinner
(q) What change takes place in an unstable nucleus when it emits a beta particle?
a neutron changes into a proton / atomic number increases by 1 and an electron (that is emitted) first correct
(r) Figure 3 represents the last two stages of a radioactive decay chain. Identify the last isotope of the chain which is formed when a bismuth–211 nucleus emits an alpha particle, and then its daughter nucleus (D) emits a beta particle.
“lead / Pb 207”Part
What is refraction of light?
bending (of light) as it passes from one medium into another
State Snell’s law of refraction.
sin𝑖/sin𝑟 = constant or n or k or μ
Alternative form for Snell’s law.
sine of angle of incidence proportional to sine of angle of refraction
Describe, with the aid of a labelled diagram, an experiment to measure the refractive index of a rectangular block of glass.
incident ray and refracted ray using pins or ray box or laser; measure angle of incidence and angle of refraction; average of values of sini ÷ sinr / refractive index is slope of graph of sini versus sinr
State whether a change occurs in its speed,
yes
State whether a change occurs in its frequency,
no
State whether a change occurs in its wavelength when a light wave undergoes refraction.
yes
Distinguish between a real and a virtual image.
real: caused by actual intersection of light rays / can be formed on a screen / object on one side of lens and image on other side; virtual: caused by apparent intersection of light rays / cannot be formed on a screen / object and image on same side of lens
Draw a diagram to show the formation of a virtual, upright, magnified image by a convex (converging) lens.
2 rays refracted; virtual paths to give upright, magnified image
An object is placed 4 cm from a convex (converging) lens. A virtual image is formed 5 cm from the lens. Calculate the focal length of the lens.
1/f = 1/u + 1/v; 1/f = 1/4 + 1/(-5); 1/f = 1/4 - 1/5 → 1/f = 1/20 → f = 20 cm
Identify the phenomenon that confines the laser light to the stream of water.
total internal reflection
What is meant by the critical angle of a material?
angle of incidence (in the denser medium) when the angle of refraction is 90° / beyond which rays are totally reflected (at boundary)
Calculate the critical angle for water if the refractive index for water is 1.33.
“n = 1/sin𝑐 or 1.33 = 1/sin𝑐 or sin𝑐 = 1/1.33 or sinc = 0.7519”Part
Distinguish between the mass and the weight of an object.
mass is the amount of matter in an object / mass is the measure of resistance to movement / mass is the measure of inertia / mass measured in kilograms or kg / mass does not change with position / mass is a scalar quantity; weight is the force of gravity on an object / weight is mass × acceleration due to gravity / weight is mass × local acceleration of free fall / W = mg / weight measured in newtons or N / weight may change with position / weight is a vector quantity
State Newton’s law of universal gravitation.
force between (any) two (point) masses is proportional to the product of the masses and inversely proportional to the square of the distance between them or their centres; F = GMm/d^2 or F ∝ Mm/d^2
Derive an expression for the relationship between g, the acceleration due to gravity, and G, the gravitational constant.
F = GMm/d^2 and F = mg → GMm/d^2 = mg; g = GM/d^2 or G = gd^2/M
Calculate the mass of Pluto. Acceleration = 0.620 m/s², radius = 1.19 × 10^6 m.
6.6742 × 10^-11 M / (1.19 × 10^6)^2 = 0.620; (M =) 1.3(15) × 10^22 kg
Calculate the mass of Charon.
GM/d^2 = Gm/x^2; M/d^2 = m/x^2 / 1.315 × 10^22 / (1.45 × 10^7)^2 = m/(5.1 × 10^6)^2; (m =) 1.6(26) × 10^21 kg
What is a photon?
packet or unit of light or of electromagnetic energy / massless particle of energy / elementary or fundamental particle of electromagnetic radiation
What is meant by the frequency?
number of waves or oscillations or periods passing a point per second or f = 1/T
What is meant by the wavelength of a wave?
distance between two (successive) corresponding points (on a wave) / distance between two (successive) crests / distance from trough to (next) trough / distance travelled (by a wave) in one period of the cycle / λ = c/f
Calculate the wavelength of the wave associated with photons of energy 7.5 × 10–19 J.
E = hf; 7.5 × 10^-19 = 6.626 × 10^-34 × f; (f =) 7.5 × 10^-19 ÷ 6.626 × 10^-34 = 1.13 × 10^15 Hz; λ = c/f; λ = 3×10^8 / 1.13 × 10^15; (λ =) 2.65 × 10^-7 m / 265 nm
Identify this phenomenon.
photoelectric effect
Explain why only some photons cause this phenomenon.
minimum energy or minimum frequency required
In terms of subatomic particles, how does a positive charge arise on an object?
loss or emission of electron(s) / more protons than electrons
Draw separate diagrams to show the distribution of positive charge on a metal sphere mounted on an insulated stand.
charges evenly distributed around the sphere
Draw separate diagrams to show the electrical field around the sphere.
radial field lines; direction away from charge / from sphere
Give one use for a gold-leaf electroscope.
to detect charge / to estimate size of charge / to compare charge / to identify charge as positive or negative / to determine whether a material is an insulator or a conductor / to measure potential / to detect radioactivity / to show the photoelectric effect
State Coulomb’s law of force between two charges.
force between two (point) charges is proportional to the product of the charges / F ∝ Q1Q2 and inversely proportional to the square of the distance separating them / F ∝ 1/d^2 or F = 1/(4πε) * (q1q2/d^2)
What was the force between the spheres when the distance between their centres was increased to 3d?
F/9 / F ÷ 9
Categorise the nuclear reaction: 𝑈 𝟗𝟐 𝟐𝟑𝟓 + 𝑛 𝟎 𝟏 → 𝐾𝑟 𝟑𝟔 𝟑𝟗𝟐 + 𝐵𝑎 𝟓𝟔 𝟏𝟒𝟏 + 3 𝑛 𝟎 𝟏 + energy.
fission
Categorise the nuclear reaction: 2 𝐻𝑒 𝟐𝟑 → 𝐻𝑒 𝟐𝟒 + 2 𝐻 𝟏 𝟏 + energy.
fusion
Explain why a nuclear chain reaction could arise in uranium–235.
neutron(s) produced (by fission of uranium) cause(s) (more) fission (of other uranium atoms)
Give one application of fission reactions.
electricity generation or power generation or nuclear reactor / bomb or weapon / to make radioactive isotopes / to investigate structure of crystals
Calculate the mass loss in unified atomic mass units (u) for each He–4 nucleus produced.
(2 × 3.016029 =) 6.032058; (4.002603 + (2 × 1.007825)) = 6.018253; (6.032058 – 6.018253) = 0.013805
Calculate the energy in joules (J) released for each He–4 nucleus produced.
(0.013805 × 1.6605402 × 10–27) = 2.2923757 × 10–29 (kg); E = mc² / E = 2.2923757 × 10–29 × (2.99792458 × 10^8)²; (E =) 2.060284532 × 10–12 (J)
