Intro to Physics II test 2

A 60 w light bulb is in a socket supplied with 120 volts. What is the current in the bulb?

0.50 A P = IV

Three resistors connected in parallel have individual values of 4, 6, and 10 ohms. If this combination is connected in series with a 12 V battery and 2 ohm resistor, what is the current in the 10 ohm resistor?

0.59 A

A steam turbine at an electric power plant delivers 4500 kW of power to an electrical generator which converts 95% of the mechanical energy into electrical energy. What is the current delivered by the generator is it delivers 3600 v?

1.19 x 10^3 Pinput = Poutput = VI

a 500 w heater carries a current of 4 A. How much does it cost to operate the heater for 30 min is electrical energy costs 6 cent per kWh?

1.5 cents

A high voltage transmission line carries 1000 A at 700 kV for a distance of 100 miles. If the resistance in the wire is 1 ohm/mile, what is the power loss due to resistive losses?

100MW

A voltage source of 10 V is connected to a series RC circuit where R = 2 x 10^6 ohm and C = -3 mF. Find the amount of time required for the current in the circuit to decay to 5 % of its original value.

18 sec V = Vo (1 - e ^ -t/RC)

A voltage source of 10 v is connected to a series RC circuit where R = 2 x 10^6 ohm and C = 3 mF. Find the amount of time required for the current in the circuit to decay to 5% of its original value

18 seconds

A metallic conductor has a resistivity of 18 x 10^6 ohm/m. What is the resistance of a piece that is 30 m long and has uniform cross sectional area of 3 x 10^6?

180 Ω

Which will drain a battery faster, a circuit with a resistance of 10k or 1 ohm

1ohm V²/R

The current in an electron beam in a cathode ray tube is measured to be 70 microA. How many electrons hit the screen in 5 seconds? (q = 1.6 x 10^-19)

2.19 x 10^15 electrons I = ∆Q / t ∆Q = ne

If a metallic wire of cross sectional area 3 x 10^-6 carries a current of 6A and has a mobile charge density of 4.24 x 10^28 carriers/m what is the average drift velocity of the mobile charge carriers? charge value = 1.6 x 10^-19 C

2.9 x 10^-4 m/s I = nqvA

The following three appliances are connected to a 120 volt house circuit: toaster 1200 w, coffee pot 750 w, microwave 600 w. If all were operated at the same time what total current would they draw?

21 A (1200/120) + (750/120) + (600/120) = 21.25 A

The following three appliances are connected to a 120V house circuit: toaster 1200 W, coffee pot 750 w, microwave 600 w. If all were operated at the same time, what total current would they draw?

21A P = VI I = P/V 1200/120 + 750/120 + 600/120

What is the maximum number of 100 watt light bulbs you can connect in parallel in a 120 V home circuit without tripping the 20 A circuit breaker?

24 light bulbs P=VI = (120)(20) = 2400

A 20 ohm platinum wire at 20 degree celsius with a temp coefficient of resistivity of 3.9 x 10^-3 will have what resistance at 100 degree celsius

26 Ω R = Ro (1 + α∆T)

The power rating of a resistor is 0.80 W. If the value of the resistor is 400 ohm, what is the max current it can draw?

45 mA P=I²R --> 0.8 w = I² 400Ω I = .045 A --> 45 mA

A simple circuit has a total resistance of 30 ohm. if a 2.0 A current is maintained in this circuit, how much energy is dissipated in this circuit in 4 sec?

480 J

You measure a 25 V potential difference across a 5 ohm resistor. What is the current flowing through it?

5 A ∆V = IR

What is the maximum number of 60 W light bulbs you can connect in parallel in a 120 V home circuit without tripping the 30 A circuit breaker?

59

A circuit has a branch in it. If the current in each of the two paths that leave the branch is 3mA. How much current does the wire coming into the branch carry?

6 mA

A 4 ohm resistor is connected in parallel with a 12 ohm resistor and this combination is connected to a DC power supply with voltage. If the total current in this circuit is 2 A, what is the value of voltage?

6 v Parallel resistor - 4x12/4+12 = 3 R= 3 Ω I = 2 A V = IR V = 2 x 3 = 6

The heating coil of a hot water heater has a resistance of 20 ohm and operates at 210 V of electrical energy costs 5.5 cents per kWh. what does it cost to heat 200kg water from 15 to 80 degree celsius

83 cents

A current flowing through a copper wire (which is connected to a battery) is due to A. electrons being accelerated by an electric field B. positively charged particles being pushed off battery terminal C. electrons being bumped by positively charged particles

A. electrons being accelerated by an electric field

A current flowing through a copper wire (connected to a battery) is due to A. electrons being accelerated by an electric field B. positively charged particles being pushed off the battery terminal C. electrons being bumped by positively charged particles D. positively charged particles being attracted to the negative terminal of a battery

A. electrons being accelerated by an electric field.

An RC circuit is connected across a DC voltage source through an open switch. The switch is closed at t=0 s. Which of the following is a correct statement regarding this circuit? A. the charge on the capacitor after four time constants is about 98% of max value B. the charge on the capacitor after one time constant is about 25% of it max value C. the charge on the capacitor after one time constant is about 50% of its max value

A. the charge on the capacitor after four time constants is about 98% max value

Copper wire #1 has a length L and a radius b. Copper wire #2 has a length 2L and radius 2b. Which statement is true? a. The total resistance of wire 1 is twice as high as wire 2 b. The total resistance of wire 1 is twice equal to that of 2 c. the total resistance of wire 1 is twice half that of wire 2 d. the total resistance of wire 1 is 4 times high that wire 2

A. the total resistance of wire 1 ir twice as high as that of wire 2 R= pL/A

If the power developed in an electric circuit is doubled, the energy used in one second is A. halved B. doubled C. quartered D. quadrupled

B. Doubled

A circuit requires a 500 ohm resistor, but all that is available are 1 k-ohm resistors. If the 1 k-ohm resistors are in abundant supply, how can they be combined to achieve the desired resistance A. series B. parallel

B. parallel

Kirchhoff's junction rule is a statement of A. the law of conservation of momentum B. the law of conservation of charge C. the law of conservation of energy D. the law of conservation of angular momentum

B. the law of conservation of charge

Why does the sum of the currents entering a junction equal the sum of the currents leaving a junction in a loop in a closed circuit? A. capacitors tend to maintain current through them at a constant value B. the potential of the nearest battery is the potential at the junction C. charge is neither created nor destroyed at a junction D. current isn't used up after it leaves a junction E. there are no transformations of energy from one type to another in a circuit loop

C. charge is neither created nor destroyed at a junction

Light bulb A is rated at 75 W and light bulb B is rated at 100 w. Both are designed to operate at 110 V. Which statement is correct? A. the 75 w bulb has smaller resistance and greater current than 100 w bulb B. the 75 w bulb has smaller resistance and smaller current C. the 75 w bulb has greater resistance and smaller current D. the 75 w bulb has greater resistance and greater current

C. the 75 w bulb has a greater resistance and a smaller current than the 100 w bulb

A capacitor C is connected in series with a resistor R across a battery and an open switch. If a second capacitor of capacitance 2C is connected in parallel to the first, the time constant of the new RC circuit will be A. the same as before B. twice as large as before C. three times as large as before D. one-hald as large as before

C. three times as large as before

The graph shows the relationship between current and potential difference for four resistors. Which resistor has the least resistance?

D has the least resistance

Which one of the following represents the correct unit for electric power? A. J/s B. Nm/s C. W D. all the above

D. all the above

The length of a certain wire is doubled and at the same time its radius is also doubled. What is the change in the resistance of this wire? A. stays the same B. it is doubled C. it's quadrupled D. it is reduced by a factor of 2 E. It is reduced by a factor of 4

D. it is reduced by a factor of 2

T or F: If you double the diameter of a cylindrical wire, you double its conductivity but reduce its resistivity by one half

False

T or F: If a one-amp current is flowing in a wire, one electron per second flow through this wire

False 1 amp = 1 coulomb/second

T or F: When current is flowing in a metal, the electrons are moving at nearly the speed of light

False moving at drift velocity ~ 10⁻¹ cm

T or F: Ohm's law is a fundamental law of physics and is therefore obeyed by all materials

False ohmic materials only

Two wires with the same resistance have the same diameter but different lengths. If wire 1 is L1 and wire 2 is L2, how do L1 and L2 compare if wire 1 is made from copper and wire 2 from aluminum? Resistivity of copper is 1.7 x 10^-5 and aluminum is 2.82 x 10^-5

L1 = 1.7 L2 2.82 x 10^-5 / 1.7 x10^-5 = 1.658

A circuit requires a 500 ohm resistor, but al that is available are 1k ohm resistors. If the 1k ohm resistors are in abundant supply, how can they be combined to achieve the desired resistance?

Parallel

A 10 mF capacitor is charged by a 10V battery through resistance R. The capacitor reaches a potential difference of 4 V in a period of 3sec after the charging began. Find value of R

R = 587 kΩ 4=10(1 - e^ -3/R(10 x 10^-6))

Two resistors, R1 and R2 have an equivalent resistance of 690 ohm when they are connected in parallel. What are R1 and R2?

R1 = 470 , R2= 220 690 = R1 + R2 150 = [1/R1 + 1/R2]⁻¹ = R1xR2 / R1 + R2

A 9 volt battery is hooked up to two resistors in series. One has a resistance of 5 ohms, and the other has a resistance of 10 ohms. Through which resistor is energy being dissipated of the higher rate?

The 10 ohm resistor

T or F: The high potential end of a resistor is the end at which the current enters it

True

T or F: in the metal wires of a circuit, the electron current i flows from the negative to the positive end of a battery, but the current I flows from the positive to the negative end of the battery

True

T or F: the charge carriers in metals are electrons, but this is not necessarily true for other types of material

True

T or F: the direction of the current I in a metal wire is the same as the direction of the internal electric field in the wire but it is opposite to the direction the electrons are moving

True

A charge of 5 coulombs move through a circuit in 0.5 seconds. How much current is flowing through the circuit? a. 2.5 A b. 5.0 A c. 7.0 A d. 10 A

a. 10 A