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NEET Physics  Current Electricity  Practice Q & A

1. Two cities are 150 km apart. electric power is sent from one city to another city through copper wires. The fall of potential per km is 8 volt and the average resistance per km is 0.5 Ω. The power loss in the wire is

 19.2 W 19.2 kW 19.2 J 12.2 kW

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2. The thermistors are usually made of:

 metals with low temperature coefficient of resistivity metals with high temperature coefficient of resistivity metal oxides with high temperature coefficient of resistivity semiconducting materials having low temperature coefficient of resistivity

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3. A potentiometer circuit has been set up for finding the internal resistance of a given cell. The main battery, used across the potentiometer wire, has an emf of 2.0 V and a negligible internal resistance. The potentiometer wire itself is 4 m long. When the resistance, R, connected across the given cell, has values of
(i) Infinity
(ii) 9.5 Ω,
the balancing lengths on the potentiometer wire are found to be 3 m and 2.85 m, respectively. The value of internal resistance of the cell is

 0.25 Ω 0.95 Ω 0.5 Ω 0.75 Ω

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4. In a potentiometer experiment, the balancing length with a cell is 240 cm. On shunting the cell with a resistance of 2 Ω, the balancing length becomes 120 cm. The internal resistance of the cell is

 1 Ω 0.5 Ω 4 Ω 2 Ω

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5. The thermo emf of a thermocouple varies with the temperature θ of the hot junction as E = aθ + bq2 (in volts) where the ratio a/b is 700°C. If the cold junction is kept at 0°C, then the neutral temperature of the thermocouple is:

 700°C 350°C 1400°C no neutral temperature is possible for this thermocouple

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6. The supply voltage to a room is 120 V. The resistance of the lead wires is 6 Ω. A 60 W bulb is already switched on. What is the decrease of voltage across the bulb, when a 240 W heater is switched on in parallel to the bulb?

 Zero volt 2.9 volt 13.3 volt 10.04 volt

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7. Two large vertical and parallel metal plates having a separation of 1 cm are connected to a DC voltage source of potential difference X. A proton is released at rest midway between the two plates. It is found to move at 45° to the vertical JUST after release. Then X is nearly

 1 × 10–5 V 1 × 10–7 V 1 × 10–9 V 1 × 10–10 V

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8. Two heating coils of resistances 10 Ω and 20 Ω are connected in parallel and connected to a battery of emf 10 V and internal resistance 1 Ω. The power consumed by them are in the ratio

 1: 4 1: 3 2: 1 4: 1

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9. In an LCR circuit as shown below both switches are open initially. Now switch S1 is closed, S2 kept open (q is charge on the capacitor and τ = RC is Capacitive time constant). Which of the following statement is correct? circuit with open switches.png" alt="LCR circuit with open switches" style="margin:0 auto;" />

 Work done by the battery is half of the energy dissipated in the resistor At t = τ, q = CV/2 At t = 2τ, q = CV(1 – e–2) At t = τ/2, q = CV(1 – e–1)

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10. Three resistances 2 Ω, 3 Ω and 4 Ω are connected in parallel. The ratio of currents passing through them when a potential difference is applied across its ends will be

 5 : 4 : 3 6 : 3 : 2 4 : 3 : 2 6 : 4 : 3

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