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Phys 211: Electricity And Magnetism I Question Paper
Phys 211: Electricity And Magnetism I
Course:Bachelor Of Science (Computer Science) & Bachelor Of Science (Applied Computer Science)
Institution: Chuka University question papers
Exam Year:2013
CHUKA
UNIVERSITY
UNIVERSITY EXAMINATIONS
SECOND YEAR EXAMINATION FOR THE AWARD OF DEGREE OF
BACHELOR OF SCIENCE (COMPUTER SCIENCE) &
BACHELOR OF SCIENCE (APPLIED COMPUTER SCIENCE)
PHYS 211: ELECTRICITY AND MAGNETISM I
STREAMS: B.Sc. COMP.SCI & ACMP) Y2S1 TIME: 2 HOURS
DAY/DATE: WEDNESDAY 14/8/2013 8.30 A.M. – 10.30 A.M.
INSTRUCTIONS:
Answer question ONE (Compulsory) and ANY other two questions.
Question One (30 marks)
In a computer laboratory, two internet access points with equal positive charges of 3µC are separated by 13.68m. what is the electrostatic force between them. [3 marks]
Given four charges q1 , q2 , q3 and q4 placed as shown in figure 1.
Figure 1: Isolated charges
The charges are placed at distances r1, r2 and r3 from q4.
Determine the electric field experienced by charge q4 due to q1, q2 and q3. [3 marks]
Sketch the electric field pattern due to the following charges [2 marks]
A computer data acquisition card, inserted into the expansion slot in its motherboard has a resistance of 350? and operated by +5V power supply terminal. Calculate the current flowing through it. [3 marks]
State Ohm’s law of electricity. [1 mark]
State four factors that determine the magnitude of induced emf in a coil. [4 marks]
Figure 2 shows a metre bridge used to measure resistance of given resistors in a laboratory.
Figure 2: Metrebridge
When a balance is obtained, the following readings were made;
Q = 100?, AD = 42.5cm, DC = 57.5cm
Find P [3 marks]
An R – L – C series circuit is connected to an ac source of voltage 150 sin1000t.
If R = 400?, L = 0.9H and C = 2.1µF. Calculate the;
impedance of the circuit [2 marks]
(ii) peak current [2 marks]
(iii) phase angle [2 marks]
(iv) average power dissipated [2 marks]
(i) A proton beam moves through a region of space where there is a uniform magnetic field of magnitude 2T, with direction along the positive z-axis. The protons have velocity of magnitude 3 x 105ms-1 in the xz plane at an angle of 30o to the positive z-axis. Determine the force on the proton. [3 marks]
Question 2 (20 Marks)
A network data cable in figure 3 is of length L and charged with line charge density f. determine the force it exert on a charge ,q, at a perpendicular distance ,a, from the cable.
[10 marks]
In reference to 2(a), determine the force when the length of the cable is very long.
[2 marks]
Consider the arrangement of resistors in an interfacing card shown in figure 4.
Determine the;
(i) equivalent resistance in the circuit. [3 marks]
(ii) current flowing in the circuit. [2 marks]
(iii) Current flowing through the 3? resistor. [3 marks]
Question 3 (20 Marks)
Show that the electric field due to a plane distribution of charges on a disk at a point P, a distance ,a, perpendicular to the plane is given by;
E = s/(2e_o )
wheres is the surface charge density on the disc. [10 marks]
Consider the arrangement of capacitors shown in figure 5.
11µF
3µF 6µF
7µF
12V
Figure 5: Capacitor network
Calculate the;
effective capacitance in the circuit [4 marks]
(ii) charge stored in 7µF capacitor. [2 marks]
(iii) energy stored in 11µF capacitor [4 marks]
Question 4 (20 Marks)
Three point chargers q1 = 1µC, q2 = -2µC and q3 = 3µC are fixed at the positions sown in figure 6.
Figure 6: Arrangement of charges
(i) What is the potential at point P at the corner of the rectangle? [6 marks]
(ii) How much work would be needed to bring a charge q4 = 2.5µC from infinity to P? [3 marks]
(iii) What is the total potential energy of q1, q2 and q3? 4 marks]
Given resistor network in series as shown in figure 7
Show that the equivalent resistance R in the circuit is given by
R = R1 + R2 + R3 + ------------------- + Rn
I is the current flowing through the circuit. [7 marks]
Question 5 (20 Marks)
Using BiotSavart’s law, show that the magnetic field at a point P, a perpendicular distance r due to a long straight conductor of infinite length and carrying a current I
is given by;
B ?=(µ_o I)/2pr [10 marks]
Part of the circuit designed by a student in computer laboratory for UPS is given in
figure 8.
4µF
5µF 3µF
6µF
20V
Figure 8: UPS circuit
(i) Calculate the effective capacitance in the circuit. [4 marks]
(ii) Determine charge stored by the UPS. [3 marks]
(iii) How would you advice the student to arrange capacitors to store more charges. Explain. [3 marks]
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