помогите с заданиями
1. Перепишите данные предложения, определите видовременные формы глаголов. Переведите предложения на русский язык:
1. You will have unlimited liability if you start a partnership.
2. If your company fails, you will only lose the value of your shares.
3. Many of the world′s diamonds are minded in South Africa and then they are sent to Amsterdam, where they are sold to international dealers.
4. President Clinton was elected in 1992.
5. I rang her yesterday, but she wasn′t in the office.
6. All the necessary documents will be sent to you next week.
1. You (will have)---future simple active unlimited liability if you( start)-------present simple active a partnership.
2. If your company (fails),-----present simple active you (will lose)----future simple active the value of your shares.
3. Many of the world′s diamonds (are mined) in South Africa and then they (are sent) to Amsterdam, where they (are sold) to international dealers.present simple passive
4. President Clinton (was elected) in 1992.past simple passive
5. I (rang) her yesterday, but she (wasn′t i)n the office.past simple active
6. All the necessary documents (will be sent) to you next week.future simple passive
Elementary properties of superconductivity
Superconductors possess both common and individual properties
according to each kind. An example of a common property of
superconductors is that they all have exactly zero resistivity to low
applied currents when there is no magnetic field present. Individual
properties include the heat capacity and the critical temperature at
which superconductivity is destroyed.
Most of the physical properties of superconductors vary from
material to material, such as the heat capacity and the critical temperature
above which superconductivity disappears. On the other hand, there is
a class of properties that are independent of the underlying material.
Lesson 4 21
For instance, all superconductors have exactly zero resistivity to low
applied currents when there is no magnetic field present. The existence
of these “universal” properties implies that superconductivity is a
thermodynamic phase and that these distinguishing properties are
largely independent of microscopic details.
Electric cables used by the European Organization for Nuclear
Research (CERN). Regular cables (background) for 12,500 amps of
electric current used at a particle accelerator called the Large ElectronPositron
Collider (LEP); superconductive cable (foreground) for the
same amount of electric current used at the Large Hadron Collider
The simplest method to measure the electrical resistance of a
sample of some material is to place it in an electrical circuit in series
with a current source “I” and measure the resulting voltage “U” across
the sample. The resistance of the sample is given by Ohm’s law:
If the voltage is zero, then the resistance is zero, which means
that the electric current is flowing freely through the sample and the
sample is in its superconducting state.
Superconductors are also able to maintain a current with no
applied voltage whatsoever, a property exploited in superconducting
electromagnets such as those found in MRI machines. Experiments
have demonstrated that currents in superconducting coils can persist
for years without any measurable degradation. Experimental evidence
points to a current lifetime of at least 100,000 years, and theoretical
estimates for the lifetime of persistent current exceed the lifetime of
In a normal conductor, an electrical current may be visualized as a
fluid of electrons moving across a heavy ionic lattice (the conducting
material), consisting of atoms that are electrically neutral. The electrons
are constantly colliding with the ions (electrically neutral atoms) in the
lattice, and during each collision some of the energy carried by the
current is absorbed by the lattice and converted into heat (which is
essentially the vibrational kinetic energy, energy due to motion of the
lattice ions). As a result, the energy carried by the current is constantly
dissipated. This is the phenomenon of electrical resistance.
22 Introduction to the World of Physics
In superconductors, on the other hand, the electronic fluid is not
made up of individual electrons, but rather pairs of electrons called
Cooper pairs, held together by an attractive force arising from the
microscopic vibrations in the lattice. According to quantum mechanics,
this Cooper pair fluid requires a minimum amount of energy, ∆E, for
it to conduct an electrical current. Specifically, the energy supplied
to the fluid needs to be greater than the thermal energy (temperature)
of the lattice in order for superconductivity to appear. This is why
superconductivity is achieved at extremely low temperatures.
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