Question

6. A circuit with an equivalent resistance of 5.0 2 uses 125 J of energy each second. What voltage is used to power this circuit? a) 5V b) 15 V c) 25 V d) 45 V e) 625 V 7. Two cylindrical resistors, A and B, are made from two different materials and have the same resistance. Resistor A has a conductivity of A = 10 03. The resistors are manufactured with the same length. The radius of Resistor A (ra) must be: a) 0.01 18 b) 0.1 TB c) TB d) 10 r8 e) 100 rb 8. A string of holiday lights contains 100 light bulbs. When a light bulb “burns out,” the resistive filament that normally heats up and generates light melts and breaks. If the 100 light bulbs are wired in series, then when one light bulb burns out _, or if they're wired in parallel a) the other 99 bulbs will turn off the other 99 bulbs will turn off b) the other 99 bulbs will remain on the other 99 bulbs will turn off c) the other 99 bulbs will turn off the other 99 bulbs will remain on d) the other 99 bulbs will remain on the other 99 bulbs will remain on 9. Kirchhoff's Junction Rule may be used in circuit analysis, because: a) Energy cannot be created or destroyed b) Charge cannot be created or destroyed c) Linear momentum cannot be created or destroyed d) Angular momentum cannot be created or destroyed

Answer 1

Solutions :

Question (6) Solution :

Answer : (c) 25 V

Given :

Equivalent resistance (R) = 5 Ω

Power used : P = 125 J/s = 125 W

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Since, Power is given by : P = V² / R

∴ V² = P R = (125 W)(5 Ω) = 625 V²

∴ V = 25 V

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Question (7) Solution :

Given :

σ_A = 10 σ_B

Since, Resistivity of conductor is given by : ρ = 1/σ

∴ ρ_A = (0.10) ρ_B

Now, The resistance of the conductor is given by :

$R=\frac{\rho L}{A}=\frac{\rho L}{\pi r^2}$

Since, Length of the conductors are constant.

$R\propto \frac{\rho}{r^2}$

Here resistance of the conductors are same.

Therefore,

$\frac{\rho_A}{(r_A)^2}= \frac{\rho_B}{(r_B)^2}$

$\rho_A\cdot (r_B)^2=\rho_B\cdot (r_A)^2$

{(0.10) ρ_B}(r_B)² = (ρ_B) (r_A)²

r_A = 0.314 r_B

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Question (8) Solution : (c) the other 99 bulbs will turn off,  the other 99 bulbs will remain on.

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Question (9) Solution : (b) Charge can not be created or destroyed.