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The current i(t) in a simple electric circuit is modeled by the differential equation d +Ri = E(t) where time L is inductance and E(t) is the voltage at time t. Using the method of undetermined coefficients, determine the charge, 4(t), at any time t, given that L = 4,R = 12, E(t) = 4sin(2t) , i(t) = d9 and that the initial current and charge is zero [15]
Figure 0.1 shows the circuit diagram of a magnetic stimulator made by an international biomedical electronics company. The pulsed magnetic field generated by the transducer coil (represented by the inductor) can be used in a variety of medical treatments including nerve stimulation. The capacitor is precharged to a Voltage V, between 0 and 1000 V, and then at /-0 the switch S is closed to trigger the magnetic pulse.
Calculate the following assuming that the switch S and the diode D are ideal:
1. The time response of the coil current after the switch S is closed, as a function of the precharge voltage V. (Some types of stimulation require a field with a fast rise time and a slow fall time.)
2. The peak coil current for V, - 950 V.
3. The time 1, at which diode D turns on.
4. The energy dissipated in the resistor for VÃ ¢ -950 V.
i coil
+
L=11 uH
R=85 m2
Vc
C=180 uF
D
(a) For a self-bias circuit, the transistor is a silicon device, RE =200Ω, R1=10R2=10kΩ,
RC=2kΩ, β=100 and VCC= 15V. Determine the values of ICQ and VCEQ. (8 marks)
and Na = 1015
cm
à ¢ 3
QUESTION 1: (14 marks)
(a) For a self-bias circuit, the transistor is a silicon device, RE =200Ω, R1=10R2=10kΩ,
RC=2kΩ, β=100 and VCC= 15V. Determine the values of ICQ and VCEQ. (8 marks)
The revenue department of a state government employs certified public accountants (CPAs)
to audit corporate tax returns and bookkeepers to audit individual returns. CPAs are paid
$31,200 per year, while the annual salary of a bookkeeper is $18,200. Given the current
staff of CPAs and bookkeepers, a study made by the department’s economist shows that
devoting one-year of a CPAs time to auditing corporate returns results in an average
additional tax collection of $52,000. In contrast, the bookkeepers only achieve additional
tax collection of $41,600 per year of a bookkeeper’s time.
i) If the department’s objective is to maximize tax revenue collected, is the present mix
CPAs and bookkeepers optimal? Explain.
ii) If the present mix of CPAs and bookkeepers is not optimal, explain what reallocation
should be made. That is, should the department hire more CPAs and fewer bookkeepers
or vice-versa?
Mike’s shear Shop provides 4,000 hair cuts each month at average price of $5.00 per
haircut. The common costs of operating the store are $12,000 per month. The business is
considering hiring a photographer who would take pictures of customers after they had their
hair cut. The price of the photographs would be $2.50 and it estimated that 2,000 customers
would purchase the service each month. The total extra cost of the photographic service is
1,000 + 1Q per month, where Q is the number of photographs sold.
i) If the decision is to be based on incremental revenue and incremental cost, should the
service be offered? Explain.
ii) If the decision is to be made on the basis of fully distributed costs and if the $12,000 in
monthly common costs is to be apportioned based on the revenues from haircuts and
photo sold each month, should the new service be offered? Why or not?
- The electrical load in a small workshop consists of 14 lamps, each rated at 240volt, 60watt and 3 electric fire, each rated at 240, 1kw. What is the effective resistance of the load
- The electrical load in a small workshop consists of 14 lamps, each rated at 240volt, 60watt and 3 electric fire, each rated at 240, 1kw. What is the effective resistance of the load
The resistance of a given electric device is 46 ohms at 25 °C. If the temperature coefficient of resistance of the material is 0.004545 at 20°C. What is the temperature of the device when its resistance is 92 ohms?
