Explore BrainMass

work, resistance and voltage problems

(See attached file for full problem description and diagrams)

The filament of a light bulb has a resistance of 580 Ω. A voltage of 120 V is connected across the filament. How much current is in the filament?

A cylindrical copper cable carries a current of 1200 A. There is a potential difference of 1.6 X 10-2 V between two points of the cable that are 0.24 m apart. What is the radius of the cable?.

A blow-dryer and a vacuum cleaner each operate with a voltage of 120 V. The current rating of the blow-dryer is 11 A, and that of the vacuum cleaner is 4.0 A. Determine the power consumed by (a) the blow-dryer and (b) the vacuum cleaner. (c) Determine the ratio of the energy used by the blow-dryer in 15 minutes to the energy used by the vacuum cleaner in one-half hour.

An electric furnace runs nine hours a day to heat a house during January (31 days). The heating element has a resistance of 5.3 Ω and carries a current of 25 A. The cost of electricity is $0.10/kWh. Find the cost of running the furnace for the month of January.

A 36.0-Ω resistor and an 18.0-Ω resistor are connected in series across a 15.0-V battery. What is the voltage across (a) the 36.0-Ω resistor and (b) the 18.0-Ω resistor?

A new "D" battery has an emf of 1.5 V. When a wire of negligible resistance is connected between the terminals of the battery, a current of 28 A is produced. Find the internal resistance of the battery.

Two batteries, each with an internal resistance of 0.015 Ω, are connected as in the drawing. In effect, the 9.0-V battery is being used to charge the 8.0-V battery. What is the current in the circuit?

A galvanometer with a coil resistance of 12.0 Ω and a full-scale current of 0.15 mA is used with a shunt resistor to make an ammeter. The ammeter registers a maximum current of 4.00 mA. Find the equivalent resistance of the ammeter.

Determine the equivalent capacitance between A and B for the group of capacitors in the drawing.

The circuit in the drawing contains two resistors and two capacitors that are connected to a battery via a switch. When the switch is closed, the capacitors begin to charge up. What is the time constant for the charging process?


(See attached file for full problem description and diagrams)


Solution Preview

Resistance R = 580 ohm
potential difference V = 120 V
Therefore, current
I = V/R = 120/580 = 0.207 == 0.21 A --Answer

current I = 1200 A
potential difference, V = 1.6*10^(-2) V
length, L = 0.24 m
resistivity or specific resistance of copper, rho = 1.682 * 10^(-8) ohm.m

Because, resistance R = V/I = 1.6*10^(-2)/1200 = 1.33*10^(-5) ohm
R = rho*L/A
=> area of cross-section A = rho*L/R = 1.682 * 10^(-8)*0.24/1.33*10^(-5) = 3.0276*10^(-4) m^2
A = pi*r^2
=> radius, r = sqrt(A/pi) = sqrt(3.0276*10^(-4)/3.14) = 9.9*10^(-3) m --Answer

voltage V = 120 V
current in dryer, Id = 11.0 A
current in vacuum tube, Iv = 4.0 A

a.) Power consumed by dryer,
Pd = V*Id = 120*11.0 = 1320.00 W --Answer

Power consumed by vacuum cleaner,
Pv = V*Iv = 120*4.0 = 480.00 w --Answer

Energy by dryer in 15 min/energy by Vacuum cleaner in half hr = ...

Solution Summary

Work over circuits are discussed. Electricity, capacitance, voltage, resistance are explored in a variety of different questions.