Electricity and Magnetism Answers

if we charge a balloon negatively, it cling to the wall. does it mean that the wall become +vely charge? and why it falls after sometime?

As the electrons are accelerated through the second anode, the gain in kinetic energy is 1.98X10^-15J, and the speed of the electrons as they enter the region between the electric field plates is 6.60X10^7m/s. The electrons are moving to the right as they pass between the electric field plates. The plates are 2.00cm long, 2.00mm apart, and as the electrons pass between the plates, the potential difference is 4.50X10^2V. The top plate of the electric field is positive charged.
a)Determine the acceleration of the electron in the region between the deflection plates. Include both magnitude and direction in your answer.
b)Determine the vertical component of the velocity of the electrons when they emerge from the region between the plates. Include both magnitude and direction in your answer.
c)Determine the vertical displacement of the electrons as they are deflected. Include both magnitude and direction in your answer.

when there is lightning in the sky,and someone sitting in front of TV , see some temporary disconnection in tv network. what is the reason?

19) The half-life of a certain radioactive isotope is 32 hours. What fraction of the sample would remain after 16 huors?
a) 0.50
b) 0.25
c) 0.62
d) 0.71
20) A potentiometer wire of length 100cm has a resistance of 10Ê. It is connected in series to to a resistance R and a cell of emf 2V and negligible internal resistance. A source of emf of 10mV is balanced by a length of 40cm of the potentiometer wire. What is the value of the resistance R?
a) 200Ê
b) 950Ê
c) 2000Ê
d) 790Ê

17) When a copper surface is illuminated by radiation of wavelength 2537 angstrome units the value of the stopping potential is found to be 0.24volts. Calculate the work function of copper.
a) 4.48eV
b) 7.46eV
c) 3.26eV
d) 2.67eV
18) A spectral line is emitted when an atom undergoes transition between two levels with a difference in energy of 2.4eV. What is the wavelength of the line?
a) 287nm
b) 507angstrome units
c) 377angstrome units
d) 518nm

15) An RLC circuit is used to tune a radio set to receive NOUN RADIO broadcasting at 105.9MHz in the FM band. The resistance and the inductance of the circuit of the radio set are 12Ê and 1.4ÖH respectively. What capacitance should the circuit have?
a) 1.64pF
b) 1.51ÖF
c) 1.33mF
d) 2.11pF
16) The work function of a metal is 3.45eV. Calculate th maximum wavelength of a photon that can eject photelectrons from the metal
a) 1:6 10À6 m
b) 3:6 10À7 m
c) 2:4 10À8 m
d) 3:4 10À7 m

13) An ac circuit consists of a voltage source v=200sin120Ùt and a 6ÖF capacitor in series. Cal
culate the current established in the circuit
a) 0.32A
b) 1.24A
c) 0.64A
d) 2.13A

14) An RLC circiut contains an ac voltage source with rms value of 50V and has a frequency of 600Hz. Suppose that a resistance R = 20 Ê, capacitance C = 10.0 ÖF and an inductance L = 4.0mH are connected in series to the source. Find the current in the circuit and the voltmeter reading across the inductor.
a) 2.17A and 32.8V
b) 1.6A and 24.2V
c) 0.13A and 12.1V
d) 4.0A and 23.1V

11) An air-cored transformer is assumed to be 100% efficient. The ratio of the secondary turns to the primary turns is 1:20. A 240V ac supply is connected to the primary coil and a 6Ê load is connected to the secondary coil. what is the current in the primary coil?
a) 0.10A
b) 0.14A
c) 2.0A
d) 40.0A

12) A voltmeter connected across a 60Hz ac source reads 240V. Write down the expression of the instanteneous voltage as a function of time.
a) 240sin339.4t
b) 339.4sin377t
c) 377cos339.4t
d) 240cos339.4t

9) A certain generator consists of a rectangular coil of 250 turns and an area of 50cm2. The coil rotates at a speed of 100 revolutions per second in a horizontal magnetic field 0.3T. Calculate the maximum induced emf in the coil and the induced emf when the plane of the coil is inclined at an angle of 35o to the horizontal
a) 235.6V and 193.0V
b) 344.2V and 230.2V
c) 144.3V and 96.5V
d) 56.4V and 26.7V
10) At which of the following values of t is the magnitude of the emf induced in the coil a maximum if a magnetic field perpendicular to the plane of a flat coil of copper wire has a time variation of the magnetic flux density given by B=Bosin(2Ùt=T) where Bo is the peak value of the magnetic flux density and T the period
a) T/8
b) T/4
c) 3T/8
d) T/2

7 )A coil of inductance 2.0H and resistance 5Ê is connected to a 30V battery. Calculate the rate of current growth in the coil when the circuit has just been made and when the current reaches one-half of its steady-state vaule.
a)15A/s and 7.5A/s
b) 3.5A/s and 10A/s
c) 12A/s and 4.4A/s
d) 6.2A/s and 18A/s
8) A 1000-turns coil of cross-sectional area 30cm2 rotates at a frequency of 120 Hz in a magnetic field 0.1 T. Calculate the peak value of the induced emf
a) 346.4V
b) 112.3V
c) 97.6V
d) 226.2V