Engineering Answers

The substation bus bar is made up of made 1.5 inches round copper bars 30 ft long. What is the resistance of each bar?

. A one-meter of annealed copper 25 mm in diameter is drawn until its resistance is 40 times the initial resistance. Its diameter afterwards is?

A one-meter rod of 2 cm diameter is drawn until its resistance is 100 times the initial resistance. Its length afterward is?

A coil has a length of 3m having an electron density of 3.34 x 1024 e/m3 with a cross sectional area of 100 cm squared. How much current will pass through the conductor in 1hr?

 An electron gun in a TV set shoots out a beam of electrons. The beam current is 2.1µA. How many electrons strike the TV screen for 5 seconds? How much charge strikes the screen in a minute?

Determine the resistance and the power absorbed by an electric heater that uses 5.0 A when connected across 110 V.

How much charge flow through a light bulb for 3 seconds if the current through the light bulb is 0.75 A?

The current in an electric lamp is 5 A. What quantity of electricity flows towards the filament in 6 minutes?

Consider a message signal 𝑚(𝑡) with bandwidth 𝑊 = 2 𝑘𝐻𝑧 , applied to a DSB-SC modulator, s.t., 𝑠(𝑡) = 𝐴𝑐𝑚(𝑡) cos(2𝜋𝑓𝑐 𝑡). Assuming perfect synchronism between the carrier waves in the modulator and detector. a. Determine (sketch) the spectrum of the detector output when 𝑓𝑐 = 1 𝑘𝐻𝑧. (Note: 𝑀(𝑓) is shown in the figure, and 𝑀(0) = 1.) b. Find the lowest 𝑓𝑐 for which each component of the modulated wave 𝑠(𝑡) is uniquely determined by 𝑚(𝑡). Sketch the spectrum of the detector output with the lowest 𝑓𝑐 that you have required. 

The average value of an oscillating electric current over one period may be zero. For example, 2nt suppose that the current is described by a simple sinusoid: i(t) = sin 2πt/T where T is the period.

The average value of this function can be determined by the following equation:

i=∫ν0^T(2πt/T)dt/T-0 = -cos(2π) + cos0/T=0

Despite the fact that the net result is zero, such current is capable of performing work and generating heat . Therefore, electrical engineers often characterize such current by

I RMS = √1\T∫ν0^Ti^2(t)dt

where i(t) = the instantaneous current. Calculate the RMS or root-mean-square current of the waveform shown in following figure using the trapezoidal rule, Simpson's 1/3 rule, Simpson's 3/8 rule for T =1 s taking n = 6.