iGCSE Physics (0625) 4.2.5 Electrical energy and electrical power-Exam Style Questions- New Syllabus
▶️ Answer/Explanation
Detailed solution:
To find the energy transferred, we use the electrical energy formula $E = IVt$.
First, convert the time from minutes to seconds: $t = 2.0 \times 60 = 120\text{ s}$.
Given values are e.m.f. $V = 2.0\text{ V}$ and current $I = 2.0\text{ A}$.
Substitute these into the equation: $E = 2.0\text{ A} \times 2.0\text{ V} \times 120\text{ s}$.
Calculating the product gives $E = 480\text{ J}$.
Therefore, the total energy transferred by the cell in the given duration is $480\text{ J}$.
▶️ Answer/Explanation
Detailed solution:
Thermal energy naturally flows from regions of higher temperature to lower temperature via conduction through solids.
Since the middle of the filament is at a very high temperature and the ends are cooler, energy is conducted toward the base.
Option B is incorrect because the rate of radiation depends on temperature; therefore, the hotter middle radiates more energy than the cooler ends.
Option C is incorrect as energy is also transferred via infrared radiation (heat) and conduction, not just visible light.
Option D is incorrect because power is proportional to the square of the voltage, $P = \frac{V^{2}}{R}$.
If the potential difference $V$ is halved to $\frac{V}{2}$, the power output becomes $\frac{1}{4}$ of its original value, assuming resistance $R$ is constant.
▶️ Answer/Explanation
Detailed solution:
First, convert all units to SI: current $I = 20\text{ mA} = 0.020\text{ A}$ and time $t = 5.0\text{ mins} = 5.0 \times 60 = 300\text{ s}$.
The electrical energy transferred is calculated using the formula $E = VIt$, where $V$ is potential difference.
Substituting the values: $E = 3.0\text{ V} \times 0.020\text{ A} \times 300\text{ s}$.
Calculating the product gives $E = 0.06 \times 300 = 18\text{ J}$.
This matches Option B exactly.