Electricity and Magnetism Answers

5) A 0.96H coil carries a current of 8.0A. Calculate the energy stored in it
a) 30.7J
b) 45.3J
c) 62.6J
d) 27.3J
6) A 1000-turn solenoid of length 20cm has a cross-sectional area of 2.0 square centimetre. Find the inductance of the coil if the core is air.
a) 1:26 10À3 H
b) 2:30 10À3 H
c) 4:66 10À3 H
d) $1.54\times10^{-3}H

3) A rod of 5.0m length is held horizontally and with its axis in an east-west direction. It is allowed to fall straight down. What is the emf induced in it when its speed is 3.0m/s if the earth's magnetic field is 0:60 10À4 T with a dip angle of 53 degrees?
a) 5:4 10À4 V
b) 3:6 10À3
c) 2:0 10À5
d) 4:2 10À4

4) A rectangular wire loop of width 4.0cm is being pulled out of a magnetic field at a constant speed of 2.0m/s. The magnetic field is 0.30T and is uniform in the region, perpendicular and into the plane of the loop. What is the induced emf in the loop?
a) 0.056V
b) 0.012V
c) 0.024V
d) 0.087V

19) A single turn coil of cross-sectional area 7.2cm^2 is in the a magnetic field of flux desity 0.45T. The field which is perpendicular to the coil, is steadily reduced to 0.0T in 5s. Calculate the induced emf.
a) 0:72ÖV
b) 0:52ÖV
c) 0:47ÖV
d) 0:65ÖV
20) What is the self - inductance of an air-core solenoid, 1m long and 0.05m in diameter, if it has 1400 turns?
a) 5.23mH
b) 4.84mH
c) 3.63mH
d) 2.42mH

17) An ammeter is suspeted of giving inaccurate readings. In order to confirm the readings, the ammeter is connected to a silver votltameter in series and a steady current is passed for one hour. The ammeter reads 0.56A and 2.0124g of silver is deposited. Wha
a) 0.06A
b) 0.11A
c)1.1A
d) 6.0A
18) The magnetic flux through each loop of a 35-loop coil is given by (3:6tÀ0:71t3) 10À2Tm2 , where the time is in seconds. Determine the induced emf at t=5.0s.
a)6.17V
b) 14.43V
c) 17.49V
d) 9.17V

15) A positive ion passes through an electric and magnetic fields which are mutually perpendicular. The electric field strength is 20.0kV/m while the magnetic flux density is 0.40T. At what speed will the ion pass through undeflected?

a) 6.0×104
m/s

b) 5.0×104
m/s

c) 7.0×104
m/s
d) $8.0\times10^{4}$$m/s

16) For how long must a steady current of 2A flow through a copper voltameter to deposit 10À3 kg of copper? Z for coper is 0.000329g/C
a) 42.1min
b) 22.6min
c) 30.2min
d) 25.3min

13) A proton is accelerated through a potential difference of 100V and the enters a region in which it is moving perpendicular to a magnetic field of flux density 0.20T. Find the radius of the circular path in which it will travel.
a) 0.9km
b) o.7km
c)0.3km
d)0.5km

14) An electron enters a uniform magnetic field 0.20T at an angle of
30o
the field. Determine the pitch of the helical path assuming its speed is
3×107
m/s
a) 90.6m
b) 37.8m
c) 56.1m
d) 46.5m

11) A rectangular coil of dimensions 20cm by 15cm lies with its plane parallel to a magnetic field of
0.5W/$m2
. The coil, carrying a current of 10A experiences a torque of 4.5Nm in the field. How many loops has the coil?
a) 100
b)60
c) 30
d) 20

12) An electric feild of 50kV/m is perpendicular to a magnetic field 0.25T. What is the velocity of a charge whose initial of motion is perpendicular to both fields and which passes through the fields undeflected?

a) 3×10
m/s

b) 2×10
m/s

c) 4×10
m/s

d) 5×10
m/s

9) One end of a simple rectangular wire-loop current balance is inserted into a solenoid. A force of
3.0×10−3
N is found to act on this end when a current of 2.0A is flowing in it. If the length of the conductor forming the end of the the wire-loop is 0.
a) 0.043T
b) 0.26T
c) 0.43T
d) 0.015T

10) A staight wire 1.0m long carries a currernt of 100A at right-angles to a uniform magnetic field of 1.0T. Find the mechanical force on the wire and the power required to move it at 15m/s in a plane at right-angles to the field.
a) 100N and 1.5kW
b) 200N and 2.5kW
c) 300N and 1.4kW
d) 200N and 2.7kW

7) A capacitor of
2.0μF
is connected to a battery of 2.0V through a resistance of
10kΩ
. What is the initial current in the circuit and the current after 0.02s?

a) 0.5μA
and 0.074mA

b) 7.4A and 5.0mA

c) 0.2μA
and 0.074mA

d) 6.2μA
and 7.04mA
8) A conductor 2cm long carrying a current of 8A lies at right angles to a magnetic field of which the flux density is 1.0T. Calculate the force exerted on the conductor
a) 0.20N
b) 0.16N
c) 0.25N
d) 0.45N

3 Kirchhof's junction rule is statement of conservation of -----------
a) mass
b) energy
c) charge
d) momentum

4) A galvanometer of resistance
120Ω
a full scale deflection with a current of 0.0005A. How would you convert it to an ammeter that reads a maximum current of 5A?
a) connect
2000Ω
in parallel to it
b) connect
200.12Ω
in series to it
c) connect $20.10\Omega$$ in series to it
d) connect
0.012Ω
in parallel to it