PHYF_125

COLLEGE OF ENGINEERINGPUTRAJAYA CAMPUSFINAL EXAMINATION

TRIMESTER II 2009/2010

PROGRAMME : Foundation in Engineering

SUBJECT CODE : PHYF125

SUBJECT : Physics II

DATE : 9 February 2010

TIME : 3 hours

VENUE : Library Exam Hall

INSTRUCTIONS TO CANDIDATES:

1. This paper consists of TEN (10) questions in Part A and FIVE (5) questions in Part B in SIX (6) pages.

2. Answer ALL questions in Part A and ANY 4 questions in Part B.

3. Write ALL answers in the answer booklet provided.

4. Write answer to each question in Part B on a new page.

THIS QUESTION PAPER CONSISTS OF 7 PRINTED PAGES INCLUDING

THIS COVER PAGE.

Page 1 of 8

PHYF125, Trimester II 2009/2010

Part A: (Answer ALL questions - each question worth 2 marks)

Constants: ke = 8.99×109 Nm2C-2, o = 8.85×10-12 C2N-1m-2, μ0 = 4π×10-7 TmA-1,

me = 9.11×10-31 kg, e = 1.60×10-19 C, mp =1.67×10-27 kg, g = 9.80 ms-2

1. A bead with a mass of 0.150 g and a charge of 2.00 µC is released from rest at a

height of 0.500 m within an electric field region. The magnitude of the field is

500 NC-1 upward. Find the speed of the bead just before it strikes the ground.

2. A long conducting cylinder with radius a carries a surface charge density σ. Find

the magnitude of the electric field inside and outside the cylinder.

3. How much kinetic energy will a charge of –6.00 µC gain (in eV) if it accelerates

through a potential difference of 25.0 kV in a cathode ray tube?

4. A cardiac defibrillator is used to shock a heart that is beating erratically. A

capacitor in this device is charged to 7.00 kV and stores 1500 J of energy. What

is the capacitance?

5. The charge density in copper is 8.49 × 1028 electrons per m3. When a 1.50-A

current is present in a copper wire with a 0.40 cm2 cross-section area, find the

electron’s drift velocity in ms-1.

6. Given that ε1 = 3.50 V, ε2 = 12.5 V, R1 = 4.50 , R2 = 12.0 , C = 4.00 F, Q

= 24.0 C, and I = 3.00 A as shown in Figure 1 below. Find the potential difference VB–VA between points A and B.

Figure 1

Page 2 of 8

I

R1

R2

ε2

C-+

A

B

ε1


7. A current of 5.50 A is maintained in a single circular loop having a

circumference of 90.0 cm. An external magnetic field of 3.50 T is directed so that

the angle between the field and the plane of the loop is 25.0. Determine the

magnitude of the torque exerted on the loop by the magnetic forces acting upon

it.

8. If a = 2.00 cm, b = 5.00 cm, and I = 35.0 A, what is the magnitude of the

magnetic field at point P as shown in Figure 2?

Figure 2

9. A flat loop of wire consisting of a single turn of cross-sectional area 8.00 cm2 is

perpendicular to a magnetic field that increases uniformly in magnitude from

0.500 T to 2.50 T in 1.00 s. What is the resulting induced current if the loop has a

resistance of 2.00 Ω?

10. An inductor in the form of solenoid contains 420 turns, 16.0 cm in length, and a

cross-sectional area of 3.00 cm2. What is the uniform rate of decrease of current

through the inductor to induce an emf of 175 μV?

Page 3 of 8

I

a

b

P


Part B: (Answer ONLY 4 questions - each question worth 10 marks)

QUESTION 1

An insulating sphere of radius a carrying a charge 3Q is surrounded by a conducting

shell with inner radius a and outer radius b carrying a charge –Q as shown in

Figure 3.

(a) Find the electric field inside the insulating sphere, inside the shell and outside

the shell. [4 marks]

(b) Find the electric flux inside the insulating sphere, inside the shell and outside the

shell. [4 marks]

(c) Sketch the graph of electric flux versus radial distance, r. [2 marks]

Figure 3

QUESTION 2

(a) A capacitor C1 of 2.70 µF is connected to 857-V battery and another capacitor C2

of 6.80 µF is connected to 685.0-V battery as shown in Figure 4 (a). These

capacitors are then disconnected from their batteries. Next the two capacitors are

connected to each other as in Figure 4 (b). What will be the potential difference

and the charge on each capacitor? [6 marks]

Page 4 of 8

b3Q

–Q

C1

C1 C2

V1 V2

(a)

C2

(b)

a

C1


Figure 4

(b) Two point charges (+10.0 nC and –10.0 nC) are located 7.00 cm apart as shown

in Figure 5. Point a is 3.00 cm from the positive point charge and point b is in

the midway of the two point charges.

Figure 5

(i) What is the potential energy of a point charge of –5.70 nC when it is

placed at point a? [3 marks]

(ii) How much work would an external force have to do to move the point

charge, described in 2(b)(i), from point b to point a? [ 1 mark]

QUESTION 3

(a) State the two Kirchhoff’s rules. [2

marks]

(b) (i) Find the equivalent resistance between point A and point B as shown in

Figure 6 below if R = 20.0 . [3

marks]

(ii) Determine the magnitude of the current in each resistor if the potential

difference V across points A and B is 20.0 V. [2

marks]

(iii) Find the potential difference across each resistor. [3 marks]

Page 5 of 8

a b


Figure 6

QUESTION 4

Three wires parallel to the x axis carry currents as shown in Figure 7. If the currents

(I = 5.00 A) are to the left,

(a) find the magnitude and the direction of the magnetic field at the origin

(i) for 80.0 cm length of the short wire A with current of 1.5I; [2

marks]

(ii) for the long wire B starting from x = 0 with current of 2I; [2

marks]

(iii) for the long wire C with current of 3I; and [2

marks]

(iv) for all the three wires. [ 1 mark]

(b) What is the magnitude and direction of the magnetic force on wire A by wire C?

[3

marks]

Page 6 of 8

2R

3R 4R

5R

6RR

A

B

y = 30.0 cm

y = -20.0 cm

y = -50.0 cm

Wire A

Wire B

Wire C

y

x


Figure 7

QUESTION 5

(a) A rectangular coil with resistance R has N turns, each of length ℓ and width w as

shown in Figure 8. The coil moves into a uniform magnetic field B with

constant velocity v. What is the magnitude and direction of the total magnetic

force on the coil

(i) as it enters the magnetic field; [2

marks]

(ii) as it moves within the field; [2

marks]

(iii) as it leaves the field? [2

marks]

Figure 8

Page 7 of 8


(b) An inductor (L = 400 mH), a capacitor (C = 4.43 μF), and a resistor (R = 500 Ω)

are connected in series. A 50.0-Hz AC source produces a maximum current of

250 mA in the circuit.

(i) Calculate the required maximum voltage ΔVmax. [2

marks]

(ii) Determine the phase angle by which the current leads or lags the applied

voltage. [2

marks]

- END OF QUESTION PAPER-

Page 8 of 8

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PHYF_125