What electric field has the same energy density as a 1.0 T magnetic field? 1.0 V

Question

What electric field has the same energy density as a 1.0 T magnetic field? 1.0 V/m 3.0 Times 10^8 V/m 9.0 Times 10^16 1.1 Times 10^-17 V/m 3.3 Times 10^-9 V/m Reducing the magnetic field to 61% of its previous value changes the magnetic energy density in the field to % of its original value. 50% 71% 85% 15% 25% An ideal transformer has 2000turns on its primary and 120tums on its secondary. If the power input to the transformer is 12kW, what is the power output 0.600kW 7.20kW 12kW 10.0 kW 240 kW A series RLC circuit has resistance 200 Ohm, inductance 0.200 H, and capacitance 0.500 mu F. If the circuit is at resonance with a 120 V Vrms source, what is the average power dissipated 144 W 120 W 77.0 W 72.0 W 100 W

Explanation / Answer

Q4.

electric field density=0.5*epsilon*E^2

magnetic field density=0.5*B^2/mu

equating both,

0.5*epsilon*E^2=0.5*B^2/mu

==>E=B/sqrt(epsilon*mu)

where epsilon=electrical permitivity =8.85*10^(-12)

mu=magnetic permeability=4*pi*10^(-7)

B is given as 1 T

hence E=1/sqrt(8.85*10^(-12)*4*pi*10^(-7))=2.9986*10^8 V/m

so correct answer is option b.

Q5.magnetic energy density=0.5*B^2/mu

as B becomes 0.61*B, energy density will become 0.5*0.61^2*B^2/mu=0.18605*B^2/mu

hence ratio of original value=0.18605/0.5=0.3721=37.21%

so no option is a valid answer.

Q6. in transformer , power input=power output

hence option c is correct.

Q7.given that R=200 ohms

as the circuit is at resonance, total impedance=resistance in the circuit=200 ohms

then power dissipated=vrms^2/R=120^2/200=72 W

hence option d is correct.

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