Laboratory work: studying resonance in an alternating-current circuit
The aim is to find voltage resonance in a series R–L–C circuit by experiment. The circuit consists of an audio-frequency generator (low voltage, about 10 V), an iron-cored inductive coil (L ≈ 1 H), a bank of variable capacitors, a resistor, two multimeters and a switch. The multimeters, set to AC voltage, are connected across the capacitor and the coil. Raising the generator frequency slowly we record U_C and U_L: at first U_C > U_L, at resonance they become equal (U_C = U_L), and afterwards U_C < U_L. The frequency at which this equality holds is the experimental ν_exp. We compare it with the calculated ν_r = 1/(2π√(LC)) and find the relative error δ = |ν_r – ν_exp|/ν_r·100 %. The point where the graphs U_C(ν) and U_L(ν) cross shows the resonance frequency. Safety: only a low-voltage teaching generator, never the mains, under the teacher's supervision; change the circuit only with the switch open.
Draw the table template in your notebook: columns ν (Hz); U_C (V); U_L (V); U_C – U_L. Fill it with the example values above, draw the graph and find the crossing point. Do the real experiment only in the school laboratory with the teacher.