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physics exam important defenitions
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Gravity
Terms in this set (67)
Displacement
displacement of a particle is the length and direction of a line drawn to the particle from the origin
(translational) equilibrium*
a body in equilibrium has zero resultant force acting on it and therefore has zero acceleration OR sum of the (net) forces acting on a body is zero;
weight
the weight of an object is the gravitational attraction of a massive body (eg Earth) for that object
Newton's 1st law
Objects at rest remain at rest and objects in motion remain in motion unless acted upon by an external force.
Newton's 2nd law*
the rate of change of momentum of a body is proportional to the net force acting on it
Newton's 3rd law*
when two bodies A and B interact the force that A exerts on B is equal and opposite to the force that B exerts on A OR when a force acts on a body, an equal an opposite force acts on another body somewhere in the universe; Award 0 for "action and reaction are equal and opposite" unless they explain what is meant by the terms.
Impulse
impulse is force x time or change in momentum
work
force × distance (moved) in the direction of the force; can be regarded as a measurement of the transfer of energy
Power
the rate of working / work/time
elastic collision
a collision in which the total KE is conserved OR (a collision in which) kinetic energy is not lost / kinetic energy is conserved;
inelastic collision
a collision in which some kinetic energy is transferred to other forms (eg internal energy, sound), therefore the total KE is less after the collision than before
temperature
measure of the average kinetic energy of molecules; it is measured on a defined scale (Celsius, Kelvin etc.)
thermal equilibrium
2 bodies that are in thermal contact are in thermal equilibrium when the net heat flow between them is zero, therefore the 2 bodies must have the same temperature
Heat
energy transferred from one body to another due to a temperature difference
thermal energy
thermal energy is the KE of the component particles of an object thus measured in joules
internal energy
the sum of all random kinetic and potential energies of molecules in a system/substance OR mention of atoms/molecules/particles; sum/total of kinetic energy and «mutual/intermolecular» potential energy
heat capacity
the amount of energy/heat required to raise the temperature of a substance/object through 1K/oC
specific heat capacity
the amount of energy required to raise the temperature of unit mass through 1 K for a substance
Isobaric
vs. Isochoric
(isovolumetric) vs. Isothermal*
a process that takes place at constant pressure vs. a process that takes place at constant volume vs. change in which the temperature stays constant
pressure
the pressure experienced by a body immersed in a fluid is the (normal) force per unit area exerted by the fluid on the surface of the body
ideal gas
obeys the universal gas law / equation PV/T OR molecules are elastic spheres of negligible volume; at all values of pressure, volume and temperature or no mutual force of attraction / repulsion;
simple harmonic motion
acceleration proportional to displacement (from a fixed point) [1 mark] OR a = -ω2x with a,ω,x explained and directed towards a fixed point (or negative sign explained)
Transverse wave*
motion of the particles is perpendicular to direction of wave travel
Longitudinal wave*
a wave where the displacement of particles/oscillations of particles/movement of particles/vibrations of particles is parallel to the direction of energy transfer/wave travel/wave movement
resonance
a system resonates when a periodic force is applied to it and the frequency of the force is equal to the natural frequency of vibration of the system OR maximum amplitude of oscillation when a periodic force is applied to it and the frequency of the force is equal to the natural frequency of vibration of the system
critical angle
the angle of incidence for which the angle of refraction is 90
total internal reflection
for a ray attempting to move from a high to a low refractive index medium; the phenomena in which the angle of incidence is greater than the critical angle;
leading to a reflected but not to a refracted ray
diffraction
spreading out of a wave; when it meets an aperture/gap/slit/obstacle
dispersion
splitting/separation (of white light) into its component colours; because different frequencies have different refractive indices
conductor
material through with electric charge flows freely in the form of free electrons
field of force
region/area/volume (of space) where a mass/charge experiences a force;
electric dipole
a separation of positive and negative charges. The simplest example of this is a pair of electric charges of equal magnitude but opposite sign, separated by some (usually small) distance.
electric field strength
the force per unit charge felt by a positive test charge placed in the field OR the force exerted per unit charge; on a small positive (test) charge;
Accept either "small" or "test" or both.
current
the rate of flow of charge past a given cross-section (of the conductor)
alternating current
current in which electrons oscillate instead of moving with the same drift speed in the same direction
drift speed
the rate at which ions move along a conductor
electric potential
the work done per unit charge; in bringing a small positive charge;
from infinity to that point OR energy/work per unit charge; in bringing a small positive test charge / positive point charge from infinity / positive test charge OR
the work required per unit charge; to bring a small positive charge / positive test charge / positive point charge from infinity to the point;
emf
power supplied per unit current / energy supplied per unit charge / work done per unit charge;
magnetic field strength, magnetic field intensity, magnetic flux density) (B)
- ratio of magnetic force on a current carrying conductor to the product of the current and length of wire and sine of the angle between the current and the magnetic field (B = FB / Ilsinθ) (OR: ratio of magnetic force on a charged particle to the product of the charge and its velocity and the sine of the angle between the velocity and the magnetic field) (B = FB / qvsinθ)
ampere
the current flowing in each of two infinitely‑long parallel wires of negligible cross‑sectional area separated by a distance of one metre in a vacuum that results in a force of exactly 2 x 10‑7 N per metre of length of each wire.
Centripetal Force
a force pointing to the centre of a circular path
Centripetal Acceleration
the acceleration due to a changing direction of velocity
Newton's Law of Gravitation
* there is an attractive force between any two point/small masses;
proportional to the product of their masses; and inversely proportional to the square of their separation; [Accept formula with all terms defined.]
gravitational field strength
the force exerted per unit mass; on a point / small mass; [Nkg-1 or ms-2]
test mass
a small mass which has a negligible effect on the gravitational field in which it is placed
unified atomic mass unit
1/12 of mass of carbon 12 atom
activity
the number of radioactive disintegrations per unit time
mass defect
the mass of a nucleus is always less the total mass of its constituent nucleons, the difference in mass is called the mass defect
binding energy
energy released when a nucleus forms from constituent nucleons; (minimum) energy needed/work done to break a nucleus up into its constituent nucleons
higgs particle
the particle whose interactions with other particles gives mass to those particles
Specific Energy* /energy density
amount of available energy stored in a fuel per unit mass/per unit volume
Primary energy source vs. Secondary energy source
energy found in nature that has not yet been subject to processing of any kind such as crude oil, coal/natural gas, solar/wind energy vs. energy that has been processed and exploited to do work of some kind such as electricity or a windmill using wind energy to raise water from a well
fuel rods
rods containing the nuclear fuel in pellet or powder form. In the case of uranium, the fuel rods contain a mixture of fissionable and non-fissionable uranium
control rods
are used to remove any excess neutrons to ensure the fission reaction continues safely (may be made of cadmium or boron steel)
moderator
Most neutrons released in fission are fast neutrons, so a moderator is used to reduce their energy down to thermal levels to ensure that the fission is self-sustaining. (may be made of solid graphite or steam)
albedo
fraction of solar radiation reaching Earth that is reflected back into space OR ratio of scattered to incident intensity of radiation (NOTE: global annual mean albedo is 0.3 for Earth)
emissivity
ratio of power/intensity emitted by an object to the power/intensity emitted by a black-body at the same temperature.
modulation
The change in the two slit intensity pattern when the single slit diffraction effect is taken into account
gravitational field strength*
force exerted per unit mass; on a small / point mass
gravitational potential energy
the work done to move a body from infinity to a point in a gravitational field
gravitational potential*
the work done per unit mass; in bringing a small/point mass from infinity to a point (in the gravitational field);
(Ratio idea essential)
electric potential energy
the electric potential energy of a system of charges is the work done to move the charges from infinite separation to their current positions
electric potential*
the work done per unit charge; in bringing a small positive charge;
from infinity to that point OR energy/work per unit charge; in bringing a small positive test charge / positive point charge from infinity / positive test charge OR
the work required per unit charge; to bring a small positive charge / positive test charge / positive point charge from infinity to the point;
electric potential difference
energy per unit charge; (ratio idea necessary)
to move positive test charge between points;
magnetic flux
the magnetic flux through a region is a measure of the number of magnetic field lines passing through the region
product of normal component of magnetic field strength and area that it links / OWTTE;
magnetic flux linkage
product of number of turns in a coil and the flux through the coil
time constant
the time for the voltage/charge/current «in circuit» to drop to 1/e
or 37% of its initial value
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