INDIAN SCHOOL ALWADI ALKABIR
CLASS X11 23//8/2016
PHYSICS
ALTERNATING CURRENT AND EMWAVES WORK SHEET
1. A lamp is connected in series with a capacitor. Predict your observation for dc and ac connections. What happens in each case if the capacitance is reduced?
2.Sketch a graph showing variation of reactance of a capacitor with
frequency of the applied voltage.
3. An electrical element X when connected to an alternating voltage source, has a currentthrough it leading the voltage byп rad. Identify X
2
‘X’ is a pure capacitor.
4.In a series LCR circuit, the voltage across an inductor, a capacitor and a resistor are 30 V,30 V and 60 V respectively. What is the phase difference between the applied voltage andcurrent in the circuit?
ZERO
5.What is the power dissipation in ac circuit in which voltage and current are given by V=3OOsin[ωt+п ] & I=5 sin ωt
2
ZERO
6.A choke coil and a bulb are connected in series to an ac source. The bulb shines brightly.How does the brightness change when an iron core is inserted in the choke coil ?
7.Given belów are two electrical circuits A and B. Calculate the ratio of power factor of circuitB to the power factor of circuit A.
Cos фB = R/ZB & Cos фA = R/ZA = √10 = √2
√5Page 1 of 2
8.An inductor L of reactance XL is connected in series with a bulb B to an ac source as shown in fig. Explain briefly how does the brightness of the bulb change when (i) number of turns of the inductor is reduced and (ii) a capacitor of reactance Xc = XL is included in the circuit.
(i) When the number of turns in the inductor is reduced, the self inductance of the coil decreases; so impedance of circuit reduces and so current in the circuit increases. Thus thebrightness of the bulb [i]increases.[ii] increases
9. A series LCR circuit with R = 20 ohm, L = 1.5 H and C = 35 μF is connected to a variablefrequency 200 V ac supply. When the frequency of the supply equals the natural frequencyof the circuit, what is the average power transferred to the circuit in one complete cycle.?
Z = √ R2 + [Xc – XL]2 = 20 ohm
Current in circuit, Irrns = Erms = 10 A
R
Power factor cosф = R/Z = R//R = 1
Average power P = Irrns Erms x cosф = 200 X 10 = 2000 W
10.In a series RC circuit, R = 30ohm, C= 0.25 μF, V =100 V and ω= 1,00,000 rad/s. Find thecurrent in the circuit and calculate the voltage across the resistor and the capacitor.
XC = 1/ωc = 40 ohm.
Impedance of circuit Z = √(30)2 +(40)2 =50 ohm
Current in circuit I = V/Z = 2 A
Voltage across resistance VR = RI = 30 x 2=60 V
Voltage across capacitance, Vc = Xc I=40 x 2=80 V
ELECTROMAGNETIC WAVES
[1]Name the electromagnetic radiation to which the following wavelength belongs:[a] 10-2 m[b] 1A0
[a] micro[b] x ray or gamma ray
[2] What is the name given to the part of em wave spectrum which is used for taking photographs of earth under foggy conditions?
I.R
[3] What is the name given to the part of em wave spectrum which is used in radar Page 2 of 3
Microwaves
[4]which part of the em spectrum has the largest penetrating power? [gamma rays]
[5] Identify the part of the electromagnetic spectrum to which the following wavelengths belong: [a] 10-1 m [b] 10-12 m
[a]short radio waves[b] gamma rays
[6] The bombardment of a metal target , by high energy electrons , can result in the production of em waves.Name the waves
[x rays]
[7] Name the em wave that are widely used in the remote switches of house hold devices
[I.R]
[8][i]Name the wave which is used to kill germs in water purifiers [U.V][ii] play an important role in maintaining the Earth’s warmth[I.R]
[9] To which regions of the em wave spectrum , the following wavelengths belong?
[i]2000A0 [ii] 5000A0[iii] 10000A0[iv] 1A0
[i]u.v[ii] visible[iii] I.R[iv] x rays
[10]Write the expression for velocity of em waves in terms of permittivity & permeability.
C= 1/√µ0ε0
[11]Identify the following em radiations as per the wave lengths given below[i] 10-3 nm[ii] 10-3 m[iii]1nm
[i] gamma[ii] micro wave[iii] x-ray
[12]Identify the following em radiations as per the frequencies given below[i] 1020 Hz[ii]109 Hz[iii] 1011Hz
[i] gamma[ii] radio[iii] microwaves
[13]The frequency of oscillation of the electric field vector of a certain em wave is 5 x 1014 hz.What is the frequency of oscillation of the corresponding magnetic field vector and to which part of the em spectrum does it belong?
Same,visible
[14] Name the em radiation used for studying crystal structure of solids
[15]Aplane emwave of frequency 25Mhz travels in free space along the x direction .At a particular point in space and time the electric vector ‘E’ is 6.3v/m. Calculate the magnetic field
C = E/B or B = E/C = 6.3/ 3 x 108m/s = 2.1 x 10-8 T
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