1 AS 物理概念大全 2016 版 Unit11Wb 1Tm2 The magnitude of the induced e m f is equal to the rate of change of magnetic flux linkage the magnitude of the induced e m f is proportional to the rate of change of magnetic flux linkage Any induced current or induced e m f will be established in a direction so as to produce effects which oppose the change that is producing it Unit 28 The root mean square value of an alternating current is that steady current which delivers the same average power as the a c to a resistive load Unit 29 One electronvolt is the energy transferred when an electron travels 10 through a potential difference of one volt The threshold frequency is defined as the minimum frequency required to release electrons from the surface of a metal Unit 30 The mass defect of a nucleus is equal to the difference between the total mass of the individual separate nucleons and the mass of the nucleus The minimum energy needed to pull a nucleus apart into its separate nucleons is known as the binding energy of the nucleus The probability that an individual nucleus will decay per unit time interval is called the decay constant The activity A of a radioactive sample is the rate at which nuclei decay or disintegrate The half life t1 2of a radioisotope is the mean time taken for half of the active nuclei in a sample to decay Unit 32 Intensity is the power per unit cross sectional area 11