Which dissipates more power

The device represented by R 3 has a very low resistance, and so when it is switched on, a large current flows. This increased current causes a larger IR drop in the wires represented by R 1 , reducing the voltage across the light bulb which is R 2 , which then dims noticeably. Figure 6. Why do lights dim when a large appliance is switched on?

The answer is that the large current the appliance motor draws causes a significant drop in the wires and reduces the voltage across the light. A switch has a variable resistance that is nearly zero when closed and extremely large when open, and it is placed in series with the device it controls. Explain the effect the switch in Figure 7 has on current when open and when closed. Figure 7. A switch is ordinarily in series with a resistance and voltage source.

Ideally, the switch has nearly zero resistance when closed but has an extremely large resistance when open. Note that in this diagram, the script E represents the voltage or electromotive force of the battery. There is a voltage across an open switch, such as in Figure 7. Why, then, is the power dissipated by the open switch small? A student in a physics lab mistakenly wired a light bulb, battery, and switch as shown in Figure 8.

Explain why the bulb is on when the switch is open, and off when the switch is closed. Do not try this—it is hard on the battery! Figure 8. Knowing that the severity of a shock depends on the magnitude of the current through your body, would you prefer to be in series or parallel with a resistance, such as the heating element of a toaster, if shocked by it?

Some strings of holiday lights are wired in series to save wiring costs. An old version utilized bulbs that break the electrical connection, like an open switch, when they burn out. If one such bulb burns out, what happens to the others? If such a string operates on V and has 40 identical bulbs, what is the normal operating voltage of each?

Newer versions use bulbs that short circuit, like a closed switch, when they burn out. If such a string operates on V and has 39 remaining identical bulbs, what is then the operating voltage of each? If two household lightbulbs rated 60 W and W are connected in series to household power, which will be brighter? Suppose you are doing a physics lab that asks you to put a resistor into a circuit, but all the resistors supplied have a larger resistance than the requested value.

How would you connect the available resistances to attempt to get the smaller value asked for? Explain why resistance cords become warm and waste energy when the radio is on.

Some light bulbs have three power settings not including zero , obtained from multiple filaments that are individually switched and wired in parallel. What is the minimum number of filaments needed for three power settings? Note: Data taken from figures can be assumed to be accurate to three significant digits.

What are the largest and smallest resistances you can obtain by connecting a An W toaster, a W electric frying pan, and a W lamp are plugged into the same outlet in a A, V circuit. The three devices are in parallel when plugged into the same socket. What power would one headlight and the starter consume if connected in series to a Neglect any other resistance in the circuit and any change in resistance in the two devices.

In both parts explicitly show how you follow the steps in the Problem-Solving Strategies for Series and Parallel Resistors above. Referring to Figure 5: a Calculate P 3 and note how it compares with P 3 found in the first two example problems in this module.

Refer to Figure 6 and the discussion of lights dimming when a heavy appliance comes on. Assume negligible change in bulb resistance. A kV power transmission line carrying 5.

What is the resistance to ground of of these insulators? Figure 9. High-voltage kV transmission line carrying 5. The row of ceramic insulators provide 1. Find the power dissipated in each of these extension cords: a an extension cord having a 0. Electrons in an X-ray tube are accelerated through 1. Calculate the power of the electron beam in this tube if it has a current of An electric water heater consumes 5.

What is the cost of running it for one year if electricity costs See Figure 3. Figure 3. On-demand electric hot water heater. Heat is supplied to water only when needed.

What would be the maximum cost of a CFL such that the total cost investment plus operating would be the same for both CFL and incandescent W bulbs? Calculate the cost for hours, as in the cost effectiveness of CFL example.

Some makes of older cars have 6. Alkaline batteries have the advantage of putting out constant voltage until very nearly the end of their life. How long will an alkaline battery rated at 1. A cauterizer, used to stop bleeding in surgery, puts out 2. The average television is said to be on 6 hours per day.

Estimate the yearly cost of electricity to operate million TVs, assuming their power consumption averages W and the cost of electricity averages An old lightbulb draws only By what factor is its diameter reduced, assuming uniform thinning along its length? Neglect any effects caused by temperature differences. Calculate the power loss in a kilometer of such wire when it carries 1. Cold vaporizers pass a current through water, evaporating it with only a small increase in temperature.

One such home device is rated at 3. See Figure 4. Figure 4. This cold vaporizer passes current directly through water, vaporizing it directly with relatively little temperature increase. Integrated Concepts a What energy is dissipated by a lightning bolt having a 20,A current, a voltage of 1. Integrated Concepts What current must be produced by a Integrated Concepts How much time is needed for a surgical cauterizer to raise the temperature of 1.

Ignore heat transfer to the surroundings. Integrated Concepts Hydroelectric generators see Figure 5 at Hoover Dam produce a maximum current of 8. How many cubic meters per second are needed, assuming Figure 5. Hydroelectric generators at the Hoover dam. Integrated Concepts a Assuming Furthermore, power dissipation in resistors is considered a naturally occurring phenomenon. The fact remains that all resistors that are part of a circuit and has a voltage drop across it will dissipate electrical power.

Moreover, this electrical power converts into heat energy, and therefore all resistors have a power rating. In regards to the laws of physics, if there is an increase in voltage E , then the current I will also increase, and the power dissipation of a resistor, will, in turn, increase as well. In the field of electronics, power dissipation is also a measurement parameter that quantifies the releasing of heat within a circuit due to inefficiencies.

As I mentioned earlier, each resistor has a power rating, and in terms of design, this allows designers to assess whether or not a particular resistor will meet their design needs within a circuit. Therefore, to calculate the power dissipated by the resistor, the formulas are as follows:.

So, using the above circuit diagram as our reference, we can apply these formulas to determine the power dissipated by the resistor. Generally speaking, no; however, there are some instances where heat dissipation is a good thing.

Take, for example, electric heaters that use resistance wire such as Nichrome. Nichrome is a unique heating element due to its cost-effectiveness, resistance to the flow of electrons, strength, flexibility, resistance to oxidation, and stability in high temperatures. Also, another instance where heat dissipation is favorable is with incandescent light bulbs, which are in use as cost-effective heaters.

Overall, under normal circumstances, heat dissipation is not desirable, but on the rare occasions that it is, it will then consist of efforts to control the heat dissipation rather than moderate it. Ensure your resistor's power rating meets your circuit design needs. The peak voltage of an ac supply is V. Since resistors are positive-valued, resistors always dissipate power.

The thicker the wire, the smaller the resistance. Superconductors have zero resistivity and hence do not dissipate power. The total power is equal to the sum of the power of each component. This is the same as with series circuits.

The same voltage exists across each branch of a parallel circuit and is equal to the source voltage. The current through a parallel branch is inversely proportional to the amount of resistance of the branch. The total power in a series circuit is equal to the SUM of the power dissipated by the individual resistors.