Title Physics MCQs_compressed (1) (1).pdf ✅

Alternating-Current 1.) An ideal chock takes a current of 10 Amp when connected to an AC supply of 125 volt and 50 Hz. A pure resistor under the same conditions takes a current of 12.5 amperes. If the two are connected to an AC supply of 100volts and 40 Hz, then the current in the series combination of the above resistor and inductor is 10 Amp 12.5 Amp 20 Amp 25 Amp For series combination; and For 40 Hz frequency; 2.) The reactance of inductor is 30 at 100Hz. The value at 50Hz will be 10 15 25 30 or, 3.) 40 electric heater is connected to a 200 V, 50 Hz main supply. The peak value of electric current following in the circuit is approximately 2.5 A 5.0 A 7 A 10 A 4.) When 100 V dc is applied across a coil, a current of 1 A flows through it. When 100 V ac of 50 Hz is applied to the same coil only 0.5 A flows. The incidence of the coil is 0.55 mH 5.5 mH 0.55 H 55 mH In D.C. circuit, In A.C. circuit, 5.) In inductive coil has a resistance of 100 . When an AC signal of frequency 1000 Hz is fed to the coil, the applied voltage leads the current by 45 . What is the inductance of the coil? 4 mH 8 mH 12 mH 16 mH Z = √R2 + X2 L R = 125 12.5 = 10Ω XL = 2πfL = V I ⇒ 2πL = 125 10 × 50 = 0.25 XL = 2πfL = 0.25 × 40 =10Ω Z = √10 2 + 10 2 = 10√2 I = V Z = 100√2 10√2 = 10Amp Ω Ω Ω Ω Ω X ′ L XL = f ′ f X ′ L = 50 100 × 30 = 15Ω Ω Ims = V R = 200 40 = 5 I0 = √2 × Irms = √2 × 5 I0 = √2 × Irms = 7.07Amp ≈ 7Amp R = V I = 100 1 = 100Ω Z = V I = 100 0.5 = 200Ω ω = 2πf = 2 × 3.14 × 50 = 314rad/sec I = V √R2 + ω 2L2 ⇒ 0.5 = 100 √100 2 + (314L) 2 ∴ L = 0.55H Ω ∘ notelibraryapp.com

11.) The r.m.s. voltage of domestic electricity supply is 220 volt. Electrical appliances should be designed to withstand an instantaneous voltage of 220 V 310 V 330 V 440 V The Peak voltage of the electric signal Electrical appliances should be designed to withstand this maximum voltage. 12.) A bulb is connected first with dc and then ac of same voltage then it will shine brightly with AC DC Brightness will be in ratio 1/1.4 Equally with both Brightness Power consumed by the Bulb As and so brightness will be equal in both the cases. 13.) Alternating current is converted to direct current by rectifier dynamo transformer motor 14.) An A.C. source is connected to a resistive circuit. What is true of the following? Current leads ahead of voltage in phase. Current lags behind voltage in phase. Current and voltage are in same phase. Any of the above may be true depending upon the value of resistance. 15.) In an oscillating L-C circuit, the maximum charge on the capacitor is . The charge on the capacitor, when the energy is stored equally between the electric and magnetic field is /2 / / /3 Maximum energy stored in the capacitor, The energy is stored equally in electric and magnetic field. Therefore energy in electric field, Now, 16.) The primary winding of a transformer has 100 turns and its secondary winding has 200 turns. The primary is connected to an AC of supply of 120 V and current flowing through it is 10 A. The voltage and current in the secondary are 240 V, 5 A 240 V, 10 A 60 V, 20 A 120 V, 20 A ω = 2πf = 120; f = 120 2π ≈ 19Hz V0 = 240V; Vms = V0 √2 ≈ 170volt = √2 × 220 = 311V ∴ ∝ ∝ V 2 R Vac.rms = Vdc Rac = Rdc , Q Q Q √2 Q √3 Q Emax = Q2 2C E = 1 2 ( Q2 2C ) Q2 2C = 1 4 Q2 C ∴ Q′ = Q √2 ES = nS ⇒ ES = E × ( nS ) notelibraryapp.com