Science · X-Factor Notes
Electric Current revision notes for UPPCS Prelims.
33 revision facts
| Concept | What to remember | Asked in UPPCS |
|---|---|---|
| Electric Current | Defined as the rate of flow of electric charge in a conductor. | |
| SI Unit of Electric Current | Ampere (1 Coulomb/second). | |
| Direction of Current | Considered the direction of flow of positive charge; opposite to the direction of electron flow. | |
| Alternating Current (AC) | Electric current that reverses its direction frequently at regular intervals. | |
| Advantage of AC over DC | AC can be transmitted to long distances without much electric energy loss. This is primarily because AC voltage can be easily stepped up or down using transformers, which reduces the current and therefore decreases the resistive losses during transmission in power lines | |
| Electric Potential | Defined as the amount of work needed to move a unit charge against an electric field; it is a scalar quantity. | U.P. P.C.S. (Pre) 2021 |
| Current Flow Condition | Electric current does not flow between two properly connected charged bodies if they are having the same potential (i.e., zero potential difference). | U.P.P.S.C. (R.I.) 2014 |
| Concept | What to remember | Asked in UPPCS |
|---|---|---|
| Unit of Energy Consumption | Electricity consumption bill is based on the measurement of kilowatt hour (1 unit). | |
| Value of 1 kilowatt hour | Equal to 3.6 × 10⁶ Joule. | UPPCS (Pre) 2006 |
| Energy Consumption Calculation | Consumption (in kWh or units) = (Wattage × Hours) / 1000. E.g., 100 watt bulb for 4 hours = 0.4 unit. | U.P. Lower Sub. (Pre) 2009 |
| Energy Consumption Calculation Example | 15 bulbs, each 200 watt capacity, illuminated for 24 hours consumes 72 units. | UPPCS (Pre) 2017 |
| Ohm's Law (Resistance) | Resistance (R) is calculated as R = V/I, where V is voltage and I is current. The ratio of voltage to current is constant when physical conditions are constant. | |
| Electric Power Calculation | If both voltage (V) and current (I) are increased twice, electric power (P = V x I) increases four times. | |
| Potential of Coalesced Drops | If n small drops, each charged to V volts, coalesce to form a single large drop, its potential will be n2/3 V. | U.P. Lower Sub. (Mains) 2015 |
| Concept | What to remember | Asked in UPPCS |
|---|---|---|
| Dynamo/ Electric Generator | Converts mechanical energy into electrical energy. It works on the principle of electromagnetic induction. | UPPCS (Mains) 2009, 2012; U.P. R.O./A.R.O. (Pre) 2017 |
| Electric Motor | Converts electrical energy into mechanical energy. Works on the principle of electromagnetic induction. | U.P. Lower Sub. (Pre) 2001; U.P. R.O./A.R.O. (Pre) 2017 |
| Low Voltage Motor Operation | Electric motors operating at low voltages tend to burn out because they draw more current, which is inversely proportional to the voltage. | UPPCS (Pre) 2008 |
| Transformer | Used to step-up or step-down AC voltage. It is NOT a device used in DC circuits. | UPPCS (Pre) 2006, 2001 |
| Mobile Phone Charger | Typically uses a step down transformer (to convert, e.g., 220V AC to 9V or 10V AC). | UPPCS (Pre) 2009 |
| Rectifier | Electrical device that converts Alternating Current (AC) to Direct Current (DC). | UPPCS (Pre) 2001; U.P. U.D.A./L.D.A. (Spl.) (Mains) 2010 |
| Inverter | Electronic circuit that changes Direct Current (DC) to Alternating Current (AC). | UPPCS (Mains) 2007 |
| Artificial Satellite Energy Source | Solar cells (photovoltaic cells) convert Sun’s energy into electrical energy. | UPPCS (Pre) 2014, 2006, 2000, 2022; U.P. P.C.S. (Pre) 2016; UPPCS (Mains) 2007 |
| Concept | What to remember | Asked in UPPCS |
|---|---|---|
| Electric Bulb Filament | Made of Tungsten. | U.P.P.C.S (Pre) 2011, 2005, 1990 |
| Electric Earth Wire | Used for safety in electric apparatus. | UPPCS (Pre) 2002 |
| Electric Fuse Principle | Works on the heating effect of electric current. | |
| Electric Fuse Characteristics | Must have a low melting point and high resistance. | I.A.S. (Pre) 1998; U.P. P.C.S. (Pre) 1993 |
| Domestic Wiring Connection | Basically a parallel connection (if one appliance fails, others continue to operate). | I.A.S. (Pre) 1996 |
| Motor Car Battery | Voltage is usually 12V; capacity is expressed in ampere-hour. Electrolyte is Sulphuric acid solution; electrodes are lead (Pb) and lead dioxide (PbO₂). | I.A.S. (Pre) 1999 |
| Halogen Lamp Filament | An alloy of Tungsten and Sodium. |
| Concept | What to remember | Asked in UPPCS |
|---|---|---|
| LED Working Principle | Works on the principle of Electroluminescence. | |
| LED vs CFL | LED lamps offer longer service life and are generally more energy efficient compared to Compact Fluorescent Lamps (CFL). | |
| Heating of Metal Wire | When electric current passes through a metal wire, its temperature rises because moving electrons continuously collide with the atoms of the conductor, transferring energy. | I.A.S. (Pre) 1998 |
| India's Electrical Frequency | The electrical system in India works at a frequency of 50 Hz. | UPPCS (Pre) 2007 |
