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Q. No.A parallel plate capacitor with circular plates of radius 1 m has a capacitance of 1 nF. At t=0, it is connected for charging in series with a resistor R=1 MΩ across a 2 V battery (as shown in the figure). The magnetic field at a point P, halfway between the centre and the periphery of the plates, after t=10–3 s is:
(the charge on the capacitor at the time t is q(t)=CV[1–e(–t/𝜏)], where the time constant τ is equal to CR.) 
1. 0.74×10−13 T
2. 0.67×10−13 T
3. 0.74×10−12 T
4. 0.67×10−12 T
A plane electromagnetic wave of frequency 25 MHz travels in free space along the x-direction. At a particular point in space and time, →E0=6.3ˆj V/m. What is →B0 at this point?
1. 2.1×10−8ˆk T
2. 1.2×10−8ˆk T
3. 2.1×10−8ˆj T
4. 1.2×10−8ˆj T
| 1. | 2.16 cm,24.1 GHz | 2. | 0.29 cm,13.7 GHz |
| 3. | 3.23 cm,20.0 GHz | 4. | 1.26 cm,23.9 GHz |
By=(2×10−7)sin(0.5×103x+1.5×1011t) T.
The expression for the electric field is:
| 1. | Ez=60sin(0.5×103x+1.5×1011t) V/m |
| 2. | Ez=60sin(1.5×103x+0.5×1011t) V/m |
| 3. | Ez=55sin(0.5×103x+1.5×1011t) V/m |
| 4. | Ez=55sin(1.5×103x+0.5×1011t) V/m |
Light with an energy flux of 18 W/cm2 falls on a non-reflecting surface at normal incidence. If the surface has an area of 20 cm2, what is the average force exerted on the surface during a 30 minute time span?
1. 2.1×10−6 N
2. 1.8×10−6 N
3. 1.2×10−6 N
4. 2.1×10−5 N
Assume a bulb of efficiency 2.5% as a point source. The peak values of the electric field and magnetic field produced by the radiation coming from a 100 W bulb at a distance of 3 m are respectively:
| 1. | 2.5 V/m, 2.2×10−8 T |
| 2. | 3.6 V/m, 3.6 T |
| 3. | 4.07 V/m, 1.4×10−8 T |
| 4. | 4.2 V/m, 3.4×10−6 T |
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Q. No.
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