19.1 Electric Potential Energy: Potential Difference

An electron is placed in an electric field of 12.0 N/C to the right. What is the resulting force on the electron?

1. 1.33×10^-20 N right
2. 1.33×10^-20 N left
3. 1.92×10^-18 N right
4. 1.92×10^-18 N left

A −5.0 C charge is being forced south by a 60 N force. What are the magnitude and direction of the local electric field?

1. 12 N/C south
2. 12 N/C north
3. 300 N/C south
4. 300 N/C north

How many electrons have to be moved by a car battery containing 7.20×10⁵ J at 12 V to reduce the energy by 1%?

1. 4.80×10²⁷
2. 4.00×10²⁶
3. 3.75×10²¹
4. 3.13×10²⁰

A typical AAA battery can move 2000 C of charge at 1.5 V. How long will this run a 50 mW LED?

1. 1000 minutes
2. 120,000 seconds
3. 15 hours
4. 250 minutes

What is the internal energy of a system consisting of two point charges, one 2.0 µC, and the other −3.0 µC, placed 1.2 m away from each other?

1. −3.8×10^-2 J
2. −4.5×10^-2 J
3. 4.5×10^-2 J
4. 3.8×10^-2 J

A system has 2.00 µC charges at (50 cm, 0) and (−50 cm, 0) and a −1.00 µC charge at (0, 70 cm). As the y-coordinate of the −1.00 µC charge increases, the potential energy ___. As the y-coordinate of the −1.00 µC charge decreases, the potential energy ___.

1. increases, increases
2. increases, decreases
3. decreases, increases
4. decreases, decreases

Take a square configuration of point charges, two positive and two negative, all of the same magnitude, with like charges sharing diagonals. What will happen to the internal energy of this system if one of the negative charges becomes a positive charge of the same magnitude?

1. increase
2. decrease
3. no change
4. not enough information

A system has 2.00 µC charges at (50 cm, 0) and (−50 cm, 0) and a −1.00 µC charge at (0, 70 cm), with a velocity in the –y-direction. When the −1.00 µC charge is at (0, 0) the potential energy is at a ___ and the kinetic energy is ___.

1. maximum, maximum
2. maximum, minimum
3. minimum, maximum
4. minimum, minimum

Find the ratio of speeds of an electron and a negative hydrogen ion (one having an extra electron) accelerated through the same voltage, assuming non-relativistic final speeds. Take the mass of the hydrogen ion to be $1 . \text{67} \times \text{10}^{– \text{27}} \text{ kg} .$

Singly charged gas ions are accelerated from rest through a voltage of 13.0 V. At what temperature will the average kinetic energy of gas molecules be the same as that given these ions?

(a) What is the average power output of a heart defibrillator that dissipates 400 J of energy in 10.0 ms? (b) Considering the high-power output, why doesn’t the defibrillator produce serious burns?

A 12.0 V battery-operated bottle warmer heats 50.0 g of glass, $2.50 \times \text{10}^{\text{2}} \text{g}$ of baby formula, and $2.00 \times \text{10}^{\text{2}} \text{g}$ of aluminum from $\text{20} . 0ºC$ to $90.0ºC$. (a) How much charge is moved by the battery? (b) How many electrons per second flow if it takes 5.00 min to warm the formula? (Hint: Assume that the specific heat of baby formula is about the same as the specific heat of water.)

A battery-operated car utilizes a 12.0 V system. Find the charge the batteries must be able to move in order to accelerate the 750 kg car from rest to 25.0 m/s, make it climb a $2.00 \times \text{10}^{\text{2}} \text{m}$ high hill, and then cause it to travel at a constant 25.0 m/s by exerting a $5.00 \times \text{10}^{\text{2}} \text{N}$ force for an hour.

(a) Find the voltage near a 10.0 cm diameter metal sphere that has 8.00 C of excess positive charge on it. (b) What is unreasonable about this result? (c) Which assumptions are responsible?