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An electric circuit includes a switch, resistors, inductors, sources of constant voltage, and capacitors (see Fig. 1). All elements are ideal. The switch initially was in the open condition for infinite time. The current in the resistor R was 1 A, direct current. What is instantaneous current in this resistor:
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in the moment when switch was closed, I(0s) (for t=0 s),
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after one second, I(1s) (for t=1 s) after the moment, when the switch was closed.
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To which final value I(∞) (for t → ∞) does the current approach with the closed switch ?
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What is the Math expression of the function I(t) ?
Fig. 1
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Resonance
Resonance in AC circuits implies a special frequency determined by the values of the resistance , capacitance , and inductance . For series resonance the condition of resonance is straightforward and it is characterized by minimum impedance and zero phase. Parallel resonance , which is more common in electronic practice, requires a more careful definition.
Series Resonance
The resonance of a series RLC circuit occurs when the inductive and capacitive reactances are equal in magnitude but cancel each other because they are 180 degrees apart in phase. The sharp minimum in impedance which occurs is useful in tuning applications. The sharpness of the minimum depends on the value of R and is characterized by the "Q" of the circuit.
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Britain says no calculators for math tests
Published: Nov. 9, 2012 at 6:44 PM
LONDON, Nov. 9 (UPI) --
The British government says 11-year-old students taking primary school math tests will be banned from using calculators beginning in 2014.
Education and Childcare Minister Elizabeth Truss said an over-reliance on calculators meant children were not being given a strong grounding in mental and written arithmetic, and students should only use calculators once they have a grasp of basic mathematical skills.
"All young children should be confident with methods of addition, subtraction, times tables and division before they pick up the calculator to work out more complex sums," Truss said.
Teaching unions responded, calling the ban "a retrograde step."
"It is entirely appropriate for children in primary school to learn to use a range of tools to solve math problems and the skill of deciding which tool and method to use for a particular problem is an important one," said Christine Blower, general secretary of the National Union of Teachers.
"It may not be appropriate to use calculators for the whole of the math test paper, but it is a retrograde step to ban them completely as it will diminish the skills set for primary pupils and leave them floundering in secondary school," she said.
The government's move follows its review of calculator use in primary schools, the BBC reported.
Read more: http://www.upi.com/Science_News/Technology/2012/11...-44841352504655/#ixzz2Bmbq1MH3
Fig. 1
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