Trade Theory - Mechanical and Electrical Fundamentals
Trade Theory - Mechanical and Electrical Fundamentals
This domain checks whether a Multi-Skill Assistant Technician can apply basic mechanical and electrical principles safely at the workplace. Questions often use simple shop-floor situations rather than formal derivations.
Core rules and concepts
- Force is a push or pull (N); torque is turning effect (N·m); work is force × distance (J); power is work per second (W).
- Mechanical advantage = load/effort for a lever or pulley system; friction wastes energy and appears as heat.
- In electricity, current (A) is flow, voltage (V) is potential difference, and resistance (Ω) opposes flow.
- Ohm's law: V = IR. Series resistances add; parallel resistance is found from 1/R = 1/R1 + 1/R2.
- Electrical power: P = VI = I²R = V²/R. AC supply frequency in India is 50 Hz.
Worked example
A 12 V supply is connected to a 6 Ω resistor. Current I = V/R = 12/6 = 2 A. Power P = VI = 12 × 2 = 24 W. If two identical 6 Ω resistors are connected in parallel, total resistance is (6×6)/(6+6) = 3 Ω, so current becomes 12/3 = 4 A and total power 48 W. The reasoning matters: parallel paths lower resistance and increase current; they do not add resistance.
Traps that cost marks
Do not mix mass (kg) with weight (N); do not add parallel resistances directly; do not use V = IR for a whole circuit when only one component's voltage is known; and always check unit prefixes such as mA and kΩ.