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KOTEBE UNIVERSITY OF EDUCATION
MENELIK I SCIENCE SHARED CAMPUS
WORKSHEET 6 (PART I)
PART I: Give short answer for the following questions.
- Explain why, under static conditions, all points in a conductor must be at the same electric potential.
- Why is important to avoid sharp edges or points on conductors must be at the same electric potential?
- Rank the potential energies of the four systems of particles shown in Figure below from largest to smallest.
- (a). Describe the motion of a proton after it released from rest in a uniform electric field. (b). Describe the changes (if any) in its kinetic energy and the electric potential energy associated with the proton.
- What is the equivalent resistance for the given network shown below?{R/3}
(a). The resistivity of zinc is 5.9 × 10−^8 Ω m. Copper is a better conductor than zinc. Does this mean that copper has a higher or lower resistivity than zinc? (b). A 1 m length of copper wire of diameter 0.4 mm has a measured resistance of 0.13 Ω. What value does this give for the resistivity of copper?
- Figure below shows a series circuit with an internal resistance, r. The battery has an e.m.f. of 6 V and an internal resistance, r, of 1.5 Ω. Explain by Calculating
(a). the current it supplies to the external resistors.{Ans:0.05A} (b). the power used in the external resistors.{Ans:0.3W} (c). the percentage of the total power wasted in the internal resistance. {Ans:3.75× 10 −3W + 0.3 = 0.30375; %age in r = 1.23%} (d). the p.d. across the 40 Ω resistor. {Ans: 2v}
- What could happen to the drift velocity of the electrons in a wire and to the current in the wire if the electrons could move through it freely without resistance
- If charges flow very slowly through a metal, why does not requires several hours for a light to come on when you throw a switch? PART III. Choose the best answer from the given alternatives.
- Two negative point charge are 2m apart and repel each other with a force of 2N. When the distance between the charges is doubled, the force between them is A. four times as great C. One half as great B. twice as great D. one forth as great
- An electric field, which is constant in space, has a magnitude of 50v/m directed along the positive x-axis. A charge Q=5μc moves under the action of the electric field from the origin to the x=5cm andy=5cm. What is the potential difference in volts through which the charge moved? A. -2.5 B. -2.0 C. -1.5 D. -1. 11.Two points charges Q 1 and Q 2 having positive sign are placed on the x axis. They are separated by adistance of a and Q 1 =4Q 2. At what distance on the x axis b/n the charges &measured from charge Q 1 will the electric (^) field vanishes? A. 2a B. 2a/3 C. a/3 D. a & c
wires? A. 𝑣𝐴 = 2𝑣𝐵 B. 𝑣𝐴 = 4𝑣𝐵 C. 2 𝑣𝐴 = 𝑣𝐵 D. 4𝑣𝐴 = 𝑣𝐵
20.A metal wire of resistance R is cut into three equal pieces that are then placed
together side by side to form a new cable with a length equal to one-third the original length. What is the resistance of this new cable?
A.
1 3 R^ B.^
1 9 R^ C.^ R^ D.^ 3R
21.Which of the following statements is correct about resistivity and
conductivity? A. They are dimensionless C. They have the same SI unit B. They have direct relationship D. One is the reciprocal of the other
22.A voltmeter should be connected in parallel across a resistor in a circuit
because A. Its resistance is very small C. Its resistance is very high B. It requires high current D. It measures current
23.The terminal potential difference of a battery is the maximum when
A. The emf of the battery is the maximum B. The battery is being discharged through a wire C. There is no current flowing through the battery D. There is a steady current flowing through the battery
PART II: WORKOUT (SHOW ALL THE NECESSARY STEPS CLEARLY)
24.The p.d applied across a series combination of 40Ω and 120Ω resistors is 2400V.
What is the p.d across the 40Ω resistor? {Ans:15A}
- Calculate the value of two equal charges if theyrepel one another with a force of 0.1N when situated 50cm apart in a vacuum. {Ans: q = 1.7x10‐6C = 1.7mC}
- The following three charges are arranged as shown. Determine the net 2. force acting on thecharge on the far right (q3 = charge 3). {Ans:0.2Ni}
27.In figure what is the resultant force on the charge in the lower left corner of the
square? Assume that q=100nC.{Ans: 0.175N, θ=−15.5^0 )
28.Two charges are located on the positive x-axis of a coordinate system, as shown in figure below. Charge q1=2nC is 2cm from the origin, and charge q2=-3nC is 4cm from the origin. What is the total force exerted by these two charges on acharge q3=5nC located at the origin?{Ans: N}
29.In figure shown, locate the point atwhich the electric field is zero? Assume a =
50cm{d=30cm}
30.We have q 1 =10 nC at the origin, q 2 = 15 nC at x=4 m. What is E at y=3 m and x=0?{Ans: E =-4.8i+14.6j)N/C; E=15.4N/C; θ = 72.8^0
35.What must the magnitude of an isolated positive charge be for the electric
potential at10 cm from the charge to be +100V?{Ans:1.1Nc}
36.What is the potential at the center of the square shown in figure? Assume that
q 1 = +10nC, q 2 = −20nC, q 3 = +30nC, q 4 = +20nC and a=1m.{Ans:500V}
37.Two charges of 2μC and -6μC are located at positions (0,0) m and (0,3) m,
respectively. (i).Find the total electric potential due to these charges at point (4,0) m. (ii).How much work is required to bring a 3μCcharge from infinity to the point P? {Ans:-=i. -6.3kV; -18.9kJ}
38.Three charges are held fixed as shown in figure.What is the potential energy?
Assume that q=1× 10
C and a=10cm{Ans:-9kJ}
39.Point charge of +12× 10 -9C and -12× 10 -9C are placed 10cm part as shown in figure. a). Compute the potential at point a, b,and c.
b). Compute the potential energy of a point charge +4× 10 -9C if it is placed at points a, b, and c.{Ans: a) Va=-900V, Vb=-1930V; Vc=0; b).
Ua=-36× 10 -7J; Ub=+77× 10 -7J; Uc=0}
40.In the rectangle shown in figure, q1 = -5x
C and q2 = 2x
C calculate
the work required tomove a charge q3 = 3x
C from B to A alongthe diagonal of the rectangle.{Ans:0.414J}
41.Three resistors with values 10.0, 7.0,and 3.0 are connected in series across a 12.0V battery. For each resistor determine: (a). its current, (b) voltage drop in each resistor, and (c) electrical power dissipated.{Ans: a).0.6A, b) 6V, 4.2V, 1.8V, c)7.2W}
42.Determine the equivalent resistance between points A and B in the circuit
shown below.{Ans: 87 2 Ω^ =43.5Ω^ }
Answer key : Part II : 9D, 10A, 11D, 12C, 13C, 14C, 15D, 16A, 17D, 18C, 19D, 20A, 21D, 22C, 23C Set by:AK
