GATE EE common mistakes
GATE EE · Understand the traps and how to avoid them.
Spending the first 20–25 minutes on a handful of 2-mark Engineering Mathematics questions and leaving 1-mark General Aptitude questions untouched until the final minutes, when panic forces guesses.
Candidates treat maths as 'safe marks' and enter a tunnel, losing track of the clock because GATE has no sectional time limit; the perceived difficulty of a question is a poor guide to its mark value.
What to do instead
Adopt a fixed two-pass strategy: in pass one (roughly 60–70 minutes) sweep the whole paper and answer only questions solvable in under 90 seconds, regardless of subject; in pass two spend the remaining time on the harder ones. Practise this with full-length timed mocks so the sweep becomes automatic.
Computing the magnitude of a transfer function or phasor correctly but reporting the angle in the wrong quadrant, e.g. giving -60° when the point lies in the second quadrant and the true angle is 120°.
Candidates apply arctan(y/x) mechanically on a calculator without checking the signs of the real and imaginary parts, forgetting that the principal arctan range is only -90° to +90°.
What to do instead
Before every phase answer, sketch the complex number on an Argand diagram and adjust by 180° when the real part is negative. Verify with a quick sanity check: a pole in the left half-plane must pull the phase negative at high frequency.
Using the full-load current when computing copper losses at part load, or adding core loss and copper loss at every load level when finding maximum efficiency of a transformer or DC machine.
The efficiency formula is memorised as a single expression without the condition that iron loss is constant while copper loss scales as the square of the load fraction, so part-load problems are answered as if at rated current.
What to do instead
Write efficiency as P_out/(P_out + P_iron + x²P_cu), where x is the per-unit load. For maximum efficiency set x²P_cu = P_iron and solve for x; then compute the actual load current from x times rated current.
Applying the standard three-phase fault formula V²/X or the per-unit impedance diagram without converting every impedance to a common MVA base and to the correct side of each transformer.
Per-unit conversion is treated as a formality; candidates mix bases from generator, transformer and line data, or forget that a transformer's per-unit impedance is unchanged across its turns ratio only when the base voltages follow the same ratio.
What to do instead
Build a base table first: choose S_base and V_base at each voltage level, then convert every given per-unit impedance using Z_new = Z_old × (S_new/S_old) × (V_old/V_new)². Check that the base voltages across each transformer match its turns ratio before solving the network.
Reading a question about a DC shunt generator or motor and applying the wrong current relation, e.g. taking line current as armature current for a shunt machine, or ignoring the field current when computing developed torque.
The circuit topology of shunt, series and compound machines is not drawn out; candidates recall E = V - I_aR_a but substitute the terminal current for I_a.
What to do instead
Redraw the machine circuit every time: for a shunt machine, I_a = I_L + I_f for a generator and I_a = I_L - I_f for a motor, with I_f = V/R_f. Then apply E_b = V ± I_aR_a with the sign chosen by machine type, and use P_dev = E_b·I_a for torque.
Assuming a diode is conducting and then not verifying the assumption, producing a solution where the calculated diode current is negative or the diode voltage exceeds the forward drop.
Ideal-diode analysis is taught as a single pass; candidates pick a state, solve the linear circuit, and stop, forgetting that the assumed state must be self-consistent.
What to do instead
Use the guess-and-verify method explicitly: assume ON (replace by a 0.7 V source or short), solve, check I_D > 0; if not, assume OFF (open circuit) and check that the voltage across it is below the forward drop. State the verified state in the answer.
Computing a convolution or Fourier-series coefficient correctly in principle but dropping the limits of integration or the 1/T (or 1/2π) normalisation factor.
Under time pressure candidates memorise the shape of the formula and forget that the coefficient definition includes a normalisation, or they integrate a piecewise signal over the wrong interval.
What to do instead
Write the defining integral in full, including limits and the 1/T or 1/2π factor, before substituting numbers. For piecewise signals, split the integral at the breakpoints and add a boundary check by testing the result at a known frequency or time index.
Confusing the resolution of an instrument with its accuracy, or computing the percentage error of a measurement using the full-scale value when the question asks for the error relative to the reading.
The two error definitions are similar in form; candidates apply the first formula they recall without checking whether the reference is full-scale deflection or the measured value.
What to do instead
Keep both formulas side by side: error relative to full scale uses the range, error relative to reading uses the indicated value. Read the question for the phrase 'of full scale' or 'of the reading' and annotate it before computing.
Converting a Boolean expression or a state table into a circuit without minimising, then failing to match the options, or misreading a K-map by grouping cells that are not adjacent including wrap-around.
Candidates minimise hastily and forget that K-map edges wrap around and that grouping must use powers of two; an extra term makes the expression look different from the correct option.
What to do instead
Draw the K-map with labelled Gray-code headers, group the largest power-of-two blocks including edge wrap, and then verify the minimised expression by testing two or three input combinations against the original truth table.
In a chopper or rectifier problem, using the average output voltage formula for the wrong conduction mode, e.g. applying V_o = DV_s to a buck converter operating in discontinuous conduction mode.
The continuous-conduction formulas are the ones most rehearsed; candidates do not check whether the inductor current reaches zero before the switch turns on again.
What to do instead
First test the mode: compute the critical inductance or the boundary load current, and compare with the given L and load. Only then choose the CCM formula; for DCM use the duty-ratio-dependent relation derived from volt-second balance and state the mode in the answer.