Joule's Law of heating states that the heat (H) produced in a conductor is directly proportional to the square of the current (I), the resistance (R), and the time (t) for which the current flows. The formula is H = I^2Rt.
14692
Why is water unsuitable for extinguishing fires involving electrical equipment?
Water is a good conductor of electricity due to dissolved impurities. If used on live electrical fires, it provides a low-resistance path for current to travel from the equipment to the person holding the hose, leading to a high risk of fatal electric shock or electrocution.
14693
Why is electrical power transmitted over long distances at high voltages?
Power transmission at high voltage is utilized to minimize energy loss due to Joule heating in the transmission lines. Since power loss is given by P = I^2R, increasing the voltage allows for a lower current (I) to transmit the same amount of power, thereby significantly reducing the heat dissipation (I^2R loss) in the wires.
14694
What form of energy is stored within a rechargeable battery during the charging process?
During the charging of a rechargeable cell, electrical energy from an external source is converted into chemical potential energy through reversible electrochemical reactions. This stored chemical energy is then converted back into electrical energy when the battery is discharged to power a device.
14695
Why do electric motors often overheat and burn out when operated at voltages significantly lower than their rated capacity?
For a constant power output, current is inversely proportional to voltage (P = VI). When voltage drops, the motor must draw higher current to maintain the required power. This increased current leads to higher I^2R losses (heat generation) in the windings, which can exceed the motor's thermal insulation limits, causing it to burn out.
14696
For which of the following applications is alternating current (AC) generally considered unsuitable?
Alternating current is not suitable for charging storage batteries (like lead-acid batteries) because batteries require a unidirectional flow of electrons (direct current) to undergo the necessary electrochemical reactions. AC would cause the battery to cycle between charging and discharging, which is ineffective and potentially damaging.
14697
Calculate the total energy dissipated in Joules when a current of 1.5 Amperes flows through a 10 Ohm resistor for a duration of 1 minute.
Energy (E) is calculated as E = I^2 * R * t. Here, I = 1.5 A, R = 10 Ω, and t = 60 seconds. E = (1.5)^2 * 10 * 60 = 2.25 * 10 * 60 = 1350 Joules. Note: The option labels use 'watts' incorrectly as units for energy.
14698
Which of the following thermodynamic or thermoelectric effects is considered irreversible?
The Joule effect, or Joule heating, describes the process where the passage of an electric current through a conductor produces heat. This process is irreversible because the generated heat cannot be converted back into electrical energy without external work, unlike thermoelectric effects like Peltier or Seebeck.
14699
Which metal is commonly utilized as the filament material in an incandescent light bulb?
Tungsten is used for light bulb filaments because it possesses an exceptionally high melting point (approximately 3422°C). This allows the filament to reach the high temperatures required to emit visible light through incandescence without melting. Additionally, it has low vapor pressure at high temperatures, which prevents the filament from evaporating quickly during operation.
14700
If an electric fan rated at 300 W operates for 8 hours daily, how many units of electrical energy are consumed in one day?
Energy consumption is calculated by multiplying power (in kilowatts) by time (in hours). Power = 300 W = 0.3 kW. Energy = 0.3 kW * 8 hours = 2.4 kWh. Since 1 unit of electricity equals 1 kWh, the total consumption is 2.4 units.
