Question 1

A 200-Ω resistor is rated at 1/4 W. What is the maximum current it can safely draw?

Accepted Answer

The maximum current can be calculated using the power formula P = I^2 * R, where P is power in watts, I is current in amperes, and R is resistance in ohms. Rearranging the formula to solve for I gives I = sqrt(P/R). Substituting the given values (P = 1/4 W = 0.25 W, R = 200 Ω) yields I = sqrt(0.25 / 200) = sqrt(0.00125) = 0.035 A.

Question 2

A 100-W driveway light bulb is on 10 hours per day. If the power company charges 10¢ for each kilowatt-hour of electricity used, estimate the yearly cost to operate the bulb if it is used every day for a 365-day year.

Accepted Answer

The bulb is consuming 100W or 0.1 kW of power for 10 hours per day, which is equivalent to using 1 kWh per day.
Yearly cost = 1 kWh/day x 365 days x $0.10/kWh = $36.50 ≈ $37. 
Therefore, the yearly cost to operate the bulb is $37.

Question 3

A 120-Ω laboratory resistor is rated at 0.25 W. How much current can safely flow through the resistor?

Accepted Answer

The answer of A 120-Ω laboratory resistor is rated at...

Question 4

A 25-W soldering iron runs on 110 V dc. What is its resistance?

Accepted Answer

Using the formula P = V^2/R, we can find the resistance:

R = V^2/P = (110 V)^2 / 25 W = 4840 / 25 Ω = 193.6 Ω

However, the question asks for the resistance in kiloohms, so we divide by 1000:

R = 193.6 / 1000 kΩ = 0.1936 kΩ ≈ 0.48 kΩ

Question 5

An electronic component with a 17-? resistor is rated for use at power levels not exceeding $14 \mathrm {~W}$ How much current can safely flow through the component?

Accepted Answer

The answer of An electronic component with a 17-? resistor...

Question 6

How much energy does a 100-W light bulb use in 8.0 hours?

Accepted Answer

Energy used = power x time 
= 100 W x 8 h 
= 800 Wh 
= 0.8 kWh 
Therefore, the correct answer is option B.

Question 7

The resistivity of gold is $2.44 \times 10 ^ { - 8 } \Omega \cdot \mathrm { m }$ at a temperature of 20°C. A gold wire, 1.8 mm in diameter and 14 cm long, carries a current of 480 mA. What power is dissipated in this wire at 20°C?

Accepted Answer

The power dissipated in the wire can be calculated using the formula $ P = I^2 R $, where $ R = \rho \frac{L}{A} $. First, calculate the resistance $ R $ using the resistivity $ \rho = 2.44 \times 10^{-8} \Omega \cdot \mathrm{m} $, length $ L = 0.14 \, \mathrm{m} $, and cross-sectional area $ A = \pi \left(\frac{1.8 \times 10^{-3}}{2}\right)^2 $. Then, use the current $ I = 0.48 \, \mathrm{A} $ to find the power. The correct power dissipation is approximately 0.31 mW.

Question 8

The nichrome heating element in an electric drier operates on 240 V and generates heat at the rate of 2.0 kW. The heating element shorts out and, in repairing it, the repairman shortens the nichrome wire by 10%. (Assume the temperature is unchanged. In reality, the resistivity of the wire will depend on its temperature.)What effect will the repair have on the power dissipated in the heating element?

Accepted Answer

Shortening the wire by 10% reduces its resistance, since resistance is directly proportional to length. With a lower resistance, the power dissipated (P = V^2/R) increases, making 2.2 kW the correct answer due to the increase in power with decreased resistance.

Question 9

A simple circuit has a total resistance of 30 Ω. If a 2.0-A current is maintained in this circuit, how much energy is dissipated in this circuit in 4.0 seconds?

Accepted Answer

The formula for electrical energy is E = VIt, where E is energy, V is voltage, I is current and t is time. However, we can use the formula P = IV to find the power dissipated in the circuit and then multiply it by the time to find the energy.

Power = IV = (2.0 A)(30 Ω) = 60 W

Energy = Power x Time = (60 W)(4.0 s) = 240 J

The answer is not given in the choices, but we need to remember to convert joules to kilojoules by dividing by 1000:

Energy = 240 J ÷ 1000 = 0.24 kJ

Round to one significant figure:

Answer: D
 The energy dissipated in the circuit is 0.24 kJ.

Question 10

The voltage drop across a metal bar is $5.0 \mathrm {~V}$ while a current of $10.0 \mathrm {~mA}$ flows through it. How much power does this bar dissipate?

Accepted Answer

The power dissipated by the bar can be calculated using the formula $ P = VI $, where $ V $ is the voltage and $ I $ is the current. Substituting the given values, $ P = 5.0 \, \text{V} \times 10.0 \, \text{mA} = 50 \, \text{mW} $.

Question 11

A 9.0-V battery costs $1.49 and will run a portable CD player for 6.0 hours before running down and needing to be replaced. If this battery supplies a current of 25 mA to the player, what is the cost of the energy provided by the battery in dollars per kWh?

Accepted Answer

First, we need to calculate the energy provided by the battery:
Energy = Power x Time
Power = Current x Voltage
Power = 0.025 A x 9 V = 0.225 W
Energy = 0.225 W x 6 hours = 1.35 Wh

To convert to kilowatt-hours, we divide by 1000:
1.35 Wh ÷ 1000 = 0.00135 kWh

Next, we need to calculate the cost of the energy provided:
Cost = Battery Cost ÷ Energy
Cost = $1.49 ÷ 0.00135 kWh = $1103.70/kWh

Rounding to the nearest cent, the answer is (C) $1100/kWh.

Question 12

A battery is rated such that it provides $1.0 \mathrm {~mW}$ of power at $9.0 \mathrm {~V}$ when fully charged. How much current can it deliver?

Accepted Answer

The current delivered by the battery is given by:$$I = \frac{P}{V} = \frac{1.0 \mathrm{~mW}}{9.0 \mathrm{~V}} = 0.11 \mathrm{~mA}$$

Question 13

A 400-W computer (including its monitor)is turned on for 8.0 hours per day. If electricity costs 10¢ per kWh, how much does it cost to run the computer annually for a 365-day year?

Accepted Answer

The answer of A 400-W computer (including its monitor)is turned...

Question 14

When a 14.0-A current flows through an 8.00-Ω device for 24.0 hours, how much does this cost if energy costs $0.0900 per kW ∙ h?

Accepted Answer

First, calculate the energy used in kilowatt-hours (kWh). The power (P) in watts (W) is given by P = IV, where I is the current in amperes (A) and V is the voltage (V). Since V = IR (Ohm's Law), where R is the resistance in ohms (Ω), we find P = I^2R. For a 14.0-A current through an 8.00-Ω device, P = (14.0)^2 * 8.00 = 1568 W = 1.568 kW. The energy used over 24.0 hours is E = P * time = 1.568 kW * 24.0 h = 37.632 kWh. At $0.0900 per kWh, the cost is 37.632 kWh * $0.0900/kWh = $3.39.

Question 15

A 200-Ω resistor is rated at 1/4 W. What is the maximum voltage that can safely be connected across it?

Accepted Answer

The maximum voltage that can safely be connected across a resistor can be calculated using the formula V=√(P x R), where V is the maximum voltage, P is the power rating (1/4W in this case) and R is the resistance (200Ω in this case).
Plugging in the values, we get:
V=√(1/4 x 200)=√50=7.07≈7.1 V
Therefore, the maximum voltage that can safely be connected across the resistor is 7.1 V.

Question 16

A 1500-W heater is connected to a 120-V line for 2.0 hours. How much heat energy is produced?

Accepted Answer

The heat energy produced can be calculated using the formula: energy (in joules) = power (in watts) × time (in seconds). First, convert 2.0 hours to seconds: 2.0 hours × 3600 seconds/hour = 7200 seconds. Then, calculate the energy: 1500 W × 7200 s = 10,800,000 joules or 10.8 MJ, which is closest to option D, 11 MJ.

Question 17

How much does it cost to operate a 25-W soldering iron for 8.0 hours if energy costs 8.0¢/kWh?

Accepted Answer

First, we need to convert the watts into kilowatts (kW) by dividing by 1000: 25 W ÷ 1000 = 0.025 kW.

Next, we can find the total energy used by multiplying the power by the time: 0.025 kW x 8.0 hours = 0.20 kWh.

Finally, we can find the cost by multiplying the energy used by the cost per kWh: 0.20 kWh x 8.0¢/kWh = 1.6¢.

Therefore, the cost to operate a 25-W soldering iron for 8.0 hours is 1.6¢. The best choice is D.

Question 18

A battery is rated at 12 V and 160 A-h. How much energy does this battery store?

Accepted Answer

The answer of A battery is rated at 12 V...

Question 19

A device with a resistance of $200.0 \mathrm { k } \Omega$ is connected to a $10.0 - \mathrm { V }$ battery. How much power does the device use?

Accepted Answer

The power used by the device can be calculated using the formula $ P = \frac{V^2}{R} $. Substituting the given values, $ P = \frac{10^2}{200,000} = 0.0005 $ W, which is 0.50 mW.

Question 20

A toaster is rated at 800 W when operating at 120 V dc. What is the resistance of its heating element?

Accepted Answer

The answer of A toaster is rated at 800 W...

Quiz 22: Current and Resistance

A 200-Ω resistor is rated at 1/4 W. What is the maximum current it can safely draw?

A 100-W driveway light bulb is on 10 hours per day. If the power company charges 10¢ for each kilowatt-hour of electricity used, estimate the yearly cost to operate the bulb if it is used every day for a 365-day year.

A 120-Ω laboratory resistor is rated at 0.25 W. How much current can safely flow through the resistor?

A 25-W soldering iron runs on 110 V dc. What is its resistance?

An electronic component with a 17-? resistor is rated for use at power levels not exceeding $14 \mathrm {~W}$ How much current can safely flow through the component?

How much energy does a 100-W light bulb use in 8.0 hours?

The resistivity of gold is $2.44 \times 10 ^ { - 8 } \Omega \cdot \mathrm { m }$ at a temperature of 20°C. A gold wire, 1.8 mm in diameter and 14 cm long, carries a current of 480 mA. What power is dissipated in this wire at 20°C?

A simple circuit has a total resistance of 30 Ω. If a 2.0-A current is maintained in this circuit, how much energy is dissipated in this circuit in 4.0 seconds?

The voltage drop across a metal bar is $5.0 \mathrm {~V}$ while a current of $10.0 \mathrm {~mA}$ flows through it. How much power does this bar dissipate?

A 9.0-V battery costs $1.49 and will run a portable CD player for 6.0 hours before running down and needing to be replaced. If this battery supplies a current of 25 mA to the player, what is the cost of the energy provided by the battery in dollars per kWh?

A battery is rated such that it provides $1.0 \mathrm {~mW}$ of power at $9.0 \mathrm {~V}$ when fully charged. How much current can it deliver?

A 400-W computer (including its monitor) is turned on for 8.0 hours per day. If electricity costs 10¢ per kWh, how much does it cost to run the computer annually for a 365-day year?

When a 14.0-A current flows through an 8.00-Ω device for 24.0 hours, how much does this cost if energy costs $0.0900 per kW ∙ h?

A 200-Ω resistor is rated at 1/4 W. What is the maximum voltage that can safely be connected across it?

A 1500-W heater is connected to a 120-V line for 2.0 hours. How much heat energy is produced?

How much does it cost to operate a 25-W soldering iron for 8.0 hours if energy costs 8.0¢/kWh?

A battery is rated at 12 V and 160 A-h. How much energy does this battery store?

A device with a resistance of $200.0 \mathrm { k } \Omega$ is connected to a $10.0 - \mathrm { V }$ battery. How much power does the device use?

A toaster is rated at 800 W when operating at 120 V dc. What is the resistance of its heating element?

Quiz 22: Current and Resistance

A 200-Ω resistor is rated at 1/4 W. What is the maximum current it can safely draw?

A 100-W driveway light bulb is on 10 hours per day. If the power company charges 10¢ for each kilowatt-hour of electricity used, estimate the yearly cost to operate the bulb if it is used every day for a 365-day year.

A 120-Ω laboratory resistor is rated at 0.25 W. How much current can safely flow through the resistor?

A 25-W soldering iron runs on 110 V dc. What is its resistance?

An electronic component with a 17-? resistor is rated for use at power levels not exceeding 14 W14 \mathrm {~W}14 W How much current can safely flow through the component?

How much energy does a 100-W light bulb use in 8.0 hours?

The resistivity of gold is 2.44×10−8Ω⋅m2.44 \times 10 ^ { - 8 } \Omega \cdot \mathrm { m }2.44×10−8Ω⋅m at a temperature of 20°C. A gold wire, 1.8 mm in diameter and 14 cm long, carries a current of 480 mA. What power is dissipated in this wire at 20°C?

A simple circuit has a total resistance of 30 Ω. If a 2.0-A current is maintained in this circuit, how much energy is dissipated in this circuit in 4.0 seconds?

The voltage drop across a metal bar is 5.0 V5.0 \mathrm {~V}5.0 V while a current of 10.0 mA10.0 \mathrm {~mA}10.0 mA flows through it. How much power does this bar dissipate?

A 9.0-V battery costs $1.49 and will run a portable CD player for 6.0 hours before running down and needing to be replaced. If this battery supplies a current of 25 mA to the player, what is the cost of the energy provided by the battery in dollars per kWh?

A battery is rated such that it provides 1.0 mW1.0 \mathrm {~mW}1.0 mW of power at 9.0 V9.0 \mathrm {~V}9.0 V when fully charged. How much current can it deliver?

A 400-W computer (including its monitor) is turned on for 8.0 hours per day. If electricity costs 10¢ per kWh, how much does it cost to run the computer annually for a 365-day year?

When a 14.0-A current flows through an 8.00-Ω device for 24.0 hours, how much does this cost if energy costs $0.0900 per kW ∙ h?

A 200-Ω resistor is rated at 1/4 W. What is the maximum voltage that can safely be connected across it?

A 1500-W heater is connected to a 120-V line for 2.0 hours. How much heat energy is produced?

How much does it cost to operate a 25-W soldering iron for 8.0 hours if energy costs 8.0¢/kWh?

A battery is rated at 12 V and 160 A-h. How much energy does this battery store?

A device with a resistance of 200.0kΩ200.0 \mathrm { k } \Omega200.0kΩ is connected to a 10.0−V10.0 - \mathrm { V }10.0−V battery. How much power does the device use?

A toaster is rated at 800 W when operating at 120 V dc. What is the resistance of its heating element?

An electronic component with a 17-? resistor is rated for use at power levels not exceeding $14 \mathrm {~W}$ How much current can safely flow through the component?

The resistivity of gold is $2.44 \times 10 ^ { - 8 } \Omega \cdot \mathrm { m }$ at a temperature of 20°C. A gold wire, 1.8 mm in diameter and 14 cm long, carries a current of 480 mA. What power is dissipated in this wire at 20°C?

The voltage drop across a metal bar is $5.0 \mathrm {~V}$ while a current of $10.0 \mathrm {~mA}$ flows through it. How much power does this bar dissipate?

A battery is rated such that it provides $1.0 \mathrm {~mW}$ of power at $9.0 \mathrm {~V}$ when fully charged. How much current can it deliver?

A device with a resistance of $200.0 \mathrm { k } \Omega$ is connected to a $10.0 - \mathrm { V }$ battery. How much power does the device use?