Engineering Answers

A parallel plate capacitor is made of 250 plates separated by a

dielectric 0.0012cm thick. The effectíve size of thé plate is 12cm x

24cm. If the dielectric constant is 2.5, what is the capacitance of

this capacitor?

Each electrode of a capacitor of the electrolytic type has an area o

0.02㎡,The relative permittivity of the dielectric aim is 2.8. if the

capacitor has a capacitance of 10uf, estimate the thickness of the

dielectric film. 

A parallel-plate capacitor, having plates of 100c㎡ and has three

dielectrics 1mm each and of permittivity’s 3, 4 and 6. If the peak

voltage 2000V is applied to the plates, calculate the energy stored

in each dielectric

Find the capacitance per unit length of a cylindrical capacitor of

which the two conductors have a radius of 2.5 cm and 4.5cm and the

dielectric consist of two layers whose cylinder or contact is 2.5cm .

radius, the inner layers having a dielectric constant of 4 and the

outer 6. 

Two capacitors C1 and C2 of 1μf and 3μf are connected in parallel

across a voltage supply. At a particular instant when the applied

voltage is increasing positively, the two capacitors together draw a

current of 4A. Find the instantaneous rate of increase of potential

across them. 

test on electronic lamp manufactured by a company indicated their life span could be assumed to be normally distributed about a mean of 1750 hours with a standard derivation of 70 hours. calculate the probability that an electronic lamp purchased burn out: (1) in more than 2000 hours (2) between 1600 and 1900 hours.

The oil dielectric to be used in a parallel plate capacitor has a

relative permittivity of 2.3 and the maximum working potential

gradient in the oil is not to exceed 104 V/m. Calculate the

Approximate plate area required for a capacitance of 0.0003μF,the

Maximum working voltage being 10,000 volts.

Two slabs of material of dielectric strengths 4 and 6 and of

thickness 2mm and 5mm respectively are the inserted between the

plates of a parallel plate capacitor. Find how much the distance

between the plates should be changes so as to restore the potential

of the capacitor to its original value.

Solar radiation is incident on a semi-transparent body at a rate of 900 W/m2 . If 150 W/m2 of this incident radiation is reflected back and 225 W/m2 is transmitted across the body, determine the absorptivity of the body. 

2.1 For the circuit shown in Figure 2(a), the switch was initially at Position 2: 2.1.1 Write the mathematical expressions for the transient behavior of the voltage 𝑣𝑐 and the current 𝑖𝑐 if the capacitor was initially uncharged and the switch is thrown into position 1 at 𝑡=0 s. (5) 2.1.2 Write the mathematical expressions for the voltage and the current if the switch is moved to position 3 at 𝑡=10 ms (assume no leakage current). (5) E 24V 8kΩ 0.08µF R1 R2 C 20kΩ iC vC + - 1 2 3 Figure 2(a) E 36V 8kΩ 2H R1 R2 L 4kΩ iL vL + - vR2 + - + vR1 - Figure 2(b) Figure 2: 2.2 For the circuit in Figure 2 (b): 2.2.1 The switch is closed at 𝑡=0 s. Write the mathematical expressions for 𝑖𝐿 , 𝑣𝐿 , 𝑣𝑅1 , 𝑣𝑅2 within five time constants of the storage phase. (5) 2.2.2 The switch is opened after five time constants of the storage phase, write the mathematical expressions for 𝑖𝐿 , 𝑣𝐿 , 𝑣𝑅1 , 𝑣𝑅2 . (5) [20]