Tiêu đề A2 Physics Definitions.pdf ✅

Communication Systems Amplitude Modulation: Amplitude of carrier wave varies in synchrony with displacement of information signal. Noise: random (unwanted) signal / power that masks / added to / interferes with / distorts transmitted signal. Regeneration: Noise/distortion is removed (from the signal) the (original) signal is reformed/reproduced/recovered/restored Or Signal detected above/below a threshold creates new signal of 1s and 0s. Frequency Modulation: Frequency of carrier wave varies in synchrony with the displacement of the signal/information wave. Attenuation: (gradual) Loss of power/intensity/amplitude (not “signal”). Modulated Carrier Wave: High frequency wave the amplitude or the frequency is varied the variation represents the information signal /in synchrony with (the displacement of) the information signal. Crosslinking: Signal in one wire (pair) is picked up by a neighboring wire (pair). Parallel to serial Convertor: Receives bits all at one time transmits the bits one after another. Digital Signal: (series of) ‘highs’ and ‘lows’ / ‘on’ and ‘off’ / 1’s and 0’s / two values with no intermediate values / the values are discrete. Analogue Signal: Signal that is continuously variable. Signal has same variation (with time) as the data. Analogue to Digital Convertor: Analogue signal is sampled at (regular time) intervals sampled signal is converted into a binary number. Cross Talk: Picking up of signal in one cable from a second (nearby) cable. Thermal Physics Specific Latent Heat: (thermal) energy required to change the state of a substance per unit mass without any change of temperature. Internal Energy: The sum of random distribution of kinetic and potential energies of the atoms or molecules in a system. Thermal Equilibrium: Same temperature no (net) transfer of thermal energy (between the bodies). Specific Heat Capacity: The (thermal) energy per unit mass to raise the temperature of a substance by one degree.

difference between V– and V+ must be very small or V– must be equal to V+ Infinite Slew Rate: The output voltage is changed instantaneously as the input voltage is changed. There is no time delay between change in input and change in output. Voltage gain: gain = voltage output / voltage input Relay: Relay is used to switch on/off mains supply using a low voltage/current output Negative Feedback: Fraction of the output (signal) is added to the input (signal). Out of phase by 180° / π rad / to inverting input. Comparator: Used to compare two potentials / voltages, output depends upon which is greater. Processing Unit: Operates on / takes signal from sensing device (so that) it gives a voltage output. Magnetic Fields and Electromagnetism Field of force: Region (of space) where an object/particle experiences a force. Magnetic Field: Region (of space) / area where a force is experienced by current-carrying conductor / moving charge / permanent magnet Tesla: One tesla is when (long) straight conductor carrying current of 1 A is normal to magnetic field (for flux density 1 T,) and experiences a force of one newton per meter. Charged Particles Quantization of charge: either charge exists in discrete and equal quantities or multiples of elementary charge / e / 1.6 × 10–19 C Electromagnetic Induction Faraday’s Law: (induced) e.m.f. proportional to rate of change of magnetic flux (linkage). Lenz’s Law: Induced e.m.f./current produces effects / acts in such a direction / tends to oppose the change causing it. Magnetic Flux Density: (numerically equal to) force per unit length on straight conductor carrying unit current normal to the field. Alternating Currents Smoothing: (output) p.d. / voltage / current does not fall to zero range of (output) p.d. / voltage / current is reduced Ideal Transformer: no power loss in transformer or input power = output power. Root Mean square value of an alternating current: That value of the direct current / steady current producing same (mean) power / heating in a resistor as the alternating current.