物理专业英语
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N2 / N1 = e
B
Elastic materials
a
extension, x
Stress v = F (Pa) : Strain The Young Modulus E = f (Pa)
v
f=
X (dimensionless) L
1
length, L cross-sectional area, A
v = rω mass, m F
r
Electric circuits
Current and circuits
Charge (Q) coulomb (C) Current (I ) ampere (A) Potential difference (V) volt (V) Power (P) watt (W) Resistance (R) ohm (Ω) In series: RTotal = R1 + R2 1 coulomb is the SI unit of charge. 1 ampere is a current of 1 coulomb per second*. 1 volt is the potential difference (PD) between two points when 1 joule of electrical work is done per coulomb moving between those points. Energy dissipated per second = IV. 1 ohm is one volt per ampere: R = V/I * 1 1 1 In parallel: = +
electron ‘wave function’ energy E2 electron ‘wave function’ energy E1
+
potential well for electron in atom nucleus with positive charge
Photoelectric effect
2 Strain energy = 2 k x
TIP: compare this formula with that for energy stored in a capacitor.
force, F
material with Young’s Modulus, E sample with spring constant, k
R Total R1 R2
Cells and electromotive force (EMF)
The EMF (ε) = the energy supplied to each coulomb by the cell. Some energy transferred in external resistance R and some in internal resistance r. Electrical work done per coulomb through resistor is V = lR. Electrical work done per coulomb through cell r is v = Ir. So ε = IR + Ir. PD across external resistor V = ε – v.
2 1 1 1 Q QV = CV = 2 2 2 C 2
TIP: compare with elastic materials.
1 + 1 In series: C1 = C C2 1 Total
:
In parallel: CTotal = C1 + C2
Photons incident on a surface may cause electrons to be emitted. Maximum kinetic energy of the emitted electrons is determined by the frequency of incident radiation and the substance being illuminated.
Conservation laws
Always apply providing the entire system is taken into account: • energy is conserved, but can transfer from one form to another; • momentum is conserved.
f = 1 2r k m
displacement x x = A cos(ωt) velocity v v = –Aωsin(ωt)
amplitude A
0 time
t
maximum speed = ωA
0 time
t
acceleration a a = –A ω2 cos(ωt) = –ω2x 0
Thermal effects
Temperature T (kelvin) = t (Celsius) + 273.15 Heat ΔQ supplied to a mass m of a substance with specific heat capacity c results in a DQ temperature rise DT = mc . Atoms within a substance at temperature T typically have energy ~kBT, where kB is the Boltzmann constant. In thermal equilibrium, two states 1 and 2 differing in energy by ΔE = E2 – E1 DE . have relative populations given by a Boltzmann factor 6– kT @
time
t
Maximum speed = A (A = amplitude) Maximum acceleration = ± 2A
Energy of oscillation, E
E= 1 2 1 2 1 2 kA = kv + kx 2 2 2
energy energy X X kinetic potential
Circular motion
Assume speed is constant (but velocity changing), ~ = angular velocity (v/r) (radian/second), acceleration (toward centre) = v2/r = ~2r, T = period = time for 1 rotation T = 2r/~
Baidu Nhomakorabeaechanics
Mechanical quantities
Mass (m) kilogram (kg) Scalar The mass of an object is a measure of its inertia: the difficulty of changing its velocity.* 1 kg is the mass of the international prototype of the kilogram stored at BIPM in Paris. Force (F) newton (N) Vector An unbalanced force causes a mass to accelerate: a = F/m. 1 newton is the force required to accelerate 1 kg at 1 m s–2. The weight W of an object is the (attractive) gravitational force acting on it: W = mg. On the Earth’s surface the gravitational field strength is g = 9.8 N/kg, so 1 kg weighs approximately 9.8 N. Energy (E ) joule (J) Scalar 1 joule is the energy change when a force of 1 newton acts through 1 metre. Gravitational potential energy change = weight × vertical distance moved = m g h. Kinetic energy (KE) = ½m v2. Power (P) watt (W) Rate of transferring energy 1 watt = 1 J/s Momentum (p) mass × velocity (kg m/s) or N s Vector Force = rate of change of momentum: force × time (impulse) = momentum change Equations of motion v = u + a t : v 2 – u2 = 2 as : s = u t + ½ a t2 (for constant acceleration)
Atomic energy and line spectra
Electrons in atoms regarded as matter waves. h , De Broglie wavelength for a particle of mass m and speed v is m = mv where h is the Planck constant. Series of “allowed” energy levels E1, E2 etc and consequent characteristic spectrum.
16–19 Study Guide
Pocket physics
a handy guide for bright stars
Miscellaneous
Ideal gases
Pressure (P) pascal (Pa) : 1 Pa = 1 newton per square __ metre. where ρ is the density of the gas and c² is the mean square speed of the molecules. 1 P = t c2 3 For n moles of gas PV = nRT.
EMF ε internal resistance r voltage, V V = IR cross-sectional area, A material with resistivity, ρ ρL A
R=
Capacitors
Q is the charge displaced from one plate to the other via the circuit. Capacitance (C) farad (F): the number of coulombs displaced per volt. C = Q/V energy stored = =
photon energy hf
maximum electron energy hf–W
substance with work function W
Simple harmonic motion
Occurs when the force on an object of mass m is directed towards a point (x = 0) and its magnitude is proportional to the distance from that point. F = –k x Oscillation frequency, f
B
Elastic materials
a
extension, x
Stress v = F (Pa) : Strain The Young Modulus E = f (Pa)
v
f=
X (dimensionless) L
1
length, L cross-sectional area, A
v = rω mass, m F
r
Electric circuits
Current and circuits
Charge (Q) coulomb (C) Current (I ) ampere (A) Potential difference (V) volt (V) Power (P) watt (W) Resistance (R) ohm (Ω) In series: RTotal = R1 + R2 1 coulomb is the SI unit of charge. 1 ampere is a current of 1 coulomb per second*. 1 volt is the potential difference (PD) between two points when 1 joule of electrical work is done per coulomb moving between those points. Energy dissipated per second = IV. 1 ohm is one volt per ampere: R = V/I * 1 1 1 In parallel: = +
electron ‘wave function’ energy E2 electron ‘wave function’ energy E1
+
potential well for electron in atom nucleus with positive charge
Photoelectric effect
2 Strain energy = 2 k x
TIP: compare this formula with that for energy stored in a capacitor.
force, F
material with Young’s Modulus, E sample with spring constant, k
R Total R1 R2
Cells and electromotive force (EMF)
The EMF (ε) = the energy supplied to each coulomb by the cell. Some energy transferred in external resistance R and some in internal resistance r. Electrical work done per coulomb through resistor is V = lR. Electrical work done per coulomb through cell r is v = Ir. So ε = IR + Ir. PD across external resistor V = ε – v.
2 1 1 1 Q QV = CV = 2 2 2 C 2
TIP: compare with elastic materials.
1 + 1 In series: C1 = C C2 1 Total
:
In parallel: CTotal = C1 + C2
Photons incident on a surface may cause electrons to be emitted. Maximum kinetic energy of the emitted electrons is determined by the frequency of incident radiation and the substance being illuminated.
Conservation laws
Always apply providing the entire system is taken into account: • energy is conserved, but can transfer from one form to another; • momentum is conserved.
f = 1 2r k m
displacement x x = A cos(ωt) velocity v v = –Aωsin(ωt)
amplitude A
0 time
t
maximum speed = ωA
0 time
t
acceleration a a = –A ω2 cos(ωt) = –ω2x 0
Thermal effects
Temperature T (kelvin) = t (Celsius) + 273.15 Heat ΔQ supplied to a mass m of a substance with specific heat capacity c results in a DQ temperature rise DT = mc . Atoms within a substance at temperature T typically have energy ~kBT, where kB is the Boltzmann constant. In thermal equilibrium, two states 1 and 2 differing in energy by ΔE = E2 – E1 DE . have relative populations given by a Boltzmann factor 6– kT @
time
t
Maximum speed = A (A = amplitude) Maximum acceleration = ± 2A
Energy of oscillation, E
E= 1 2 1 2 1 2 kA = kv + kx 2 2 2
energy energy X X kinetic potential
Circular motion
Assume speed is constant (but velocity changing), ~ = angular velocity (v/r) (radian/second), acceleration (toward centre) = v2/r = ~2r, T = period = time for 1 rotation T = 2r/~
Baidu Nhomakorabeaechanics
Mechanical quantities
Mass (m) kilogram (kg) Scalar The mass of an object is a measure of its inertia: the difficulty of changing its velocity.* 1 kg is the mass of the international prototype of the kilogram stored at BIPM in Paris. Force (F) newton (N) Vector An unbalanced force causes a mass to accelerate: a = F/m. 1 newton is the force required to accelerate 1 kg at 1 m s–2. The weight W of an object is the (attractive) gravitational force acting on it: W = mg. On the Earth’s surface the gravitational field strength is g = 9.8 N/kg, so 1 kg weighs approximately 9.8 N. Energy (E ) joule (J) Scalar 1 joule is the energy change when a force of 1 newton acts through 1 metre. Gravitational potential energy change = weight × vertical distance moved = m g h. Kinetic energy (KE) = ½m v2. Power (P) watt (W) Rate of transferring energy 1 watt = 1 J/s Momentum (p) mass × velocity (kg m/s) or N s Vector Force = rate of change of momentum: force × time (impulse) = momentum change Equations of motion v = u + a t : v 2 – u2 = 2 as : s = u t + ½ a t2 (for constant acceleration)
Atomic energy and line spectra
Electrons in atoms regarded as matter waves. h , De Broglie wavelength for a particle of mass m and speed v is m = mv where h is the Planck constant. Series of “allowed” energy levels E1, E2 etc and consequent characteristic spectrum.
16–19 Study Guide
Pocket physics
a handy guide for bright stars
Miscellaneous
Ideal gases
Pressure (P) pascal (Pa) : 1 Pa = 1 newton per square __ metre. where ρ is the density of the gas and c² is the mean square speed of the molecules. 1 P = t c2 3 For n moles of gas PV = nRT.
EMF ε internal resistance r voltage, V V = IR cross-sectional area, A material with resistivity, ρ ρL A
R=
Capacitors
Q is the charge displaced from one plate to the other via the circuit. Capacitance (C) farad (F): the number of coulombs displaced per volt. C = Q/V energy stored = =
photon energy hf
maximum electron energy hf–W
substance with work function W
Simple harmonic motion
Occurs when the force on an object of mass m is directed towards a point (x = 0) and its magnitude is proportional to the distance from that point. F = –k x Oscillation frequency, f