Current Electricity - Live Session - NEET 2020Contact Number: 9667591930 / 8527521718

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A carbon resistor of (47 ± 4.7) k$\mathrm{\Omega}$ is to be marked with rings of different colours for its identification. The colour

code sequence will be

(1) Violet – Yellow – Orange – Silver

(2) Yellow – Violet – Orange– Silver

(3) Green – Orange – Violet – Gold

(4) Yellow – Green – Violet – Gold

A set of 'n' equal resistors, of value 'R' each, are connected in series to a battery of emf 'E' and internal resistance 'R'. The current drawn is I. Now, the 'n' resistors are connected in parallel to the same battery. Then the current drawn from battery becomes 10 I. The value of 'n' is

(1) 10

(2) 11

(3) 9

(4) 20

A battery consists of a variable number 'n' of identical cells (having internal resistance 'r' each) which are connected in series. The terminals of the battery are short-circuited and the current I is measured. Which of the graphs shows the correct relationship between I and n?

The resistance of a wire is ‘R’ ohm. If it is melted and stretched to ‘n’ times its original length, its new resistance will be

(1) nR

(2) $\frac{\mathrm{R}}{\mathrm{n}}$

(3) n^{2}R

(4) $\frac{\mathrm{R}}{{\mathrm{n}}^{2}}$

A potentiometer is an accurate and versatile device to make electrical measurements of E.M.F, because the method involves

(1) Cells

(2) Potential gradients

(3) A condition of no current flow through the galvanometer

(4) A combination of cells, galvanometer and resistances

The potential difference (V_{A} – V_{B}) between the points A and B in the given figure is

(1) –3 V (2) +3 V

(3) +6 V (4) +9 V

A filament bulb (500 W, 100 V) is to be used in a 230 V main supply. When a resistance R is connected in series, it works perfectly and the bulb consumes 500 W. The value of R is

(1) 230 $\mathrm{\Omega}$ (2) 46 $\mathrm{\Omega}$

(3) 26 $\mathrm{\Omega}$ (4) 13 $\mathrm{\Omega}$

A potentiometer wire is 100 cm long and a constant potential difference is maintained across it. Two cells are connected in series first to support one another and then in opposite direction. The balance points are obtained at 50 cm and 10 cm from the positive end of the wire in the two cases. The ratio of emf ’s is

(1) 3 : 2 (2) 5 : 1

(3) 5 : 4 (4) 3 : 4

The charge flowing through a resistance R varies with time t as Q = at – bt^{2}, where a and b are positive constants. The total heat produced in R is

1. $\frac{{\mathrm{a}}^{3}\mathrm{R}}{\mathrm{b}}$

2. $\frac{{\mathrm{a}}^{3}\mathrm{R}}{6\mathrm{b}}$

3. $\frac{{\mathrm{a}}^{3}\mathrm{R}}{3\mathrm{b}}$

4. $\frac{{\mathrm{a}}^{3}\mathrm{R}}{2\mathrm{b}}$

A potentiometer wire of length L and a resistance r are connected in series with a battery of e.m.f. E_{0} and a resistance r_{1}. An unknown e.m.f. E is balanced at a length l of the potentiometer wire. The e.m.f. E will be given by

1. $\frac{{\mathrm{LE}}_{0}\mathrm{r}}{\left(\mathrm{r}+{\mathrm{r}}_{1}\right)\mathrm{l}}$

2. $\frac{{\mathrm{LE}}_{0}\mathrm{r}}{{\mathrm{lr}}_{1}}$

3. $\frac{{\mathrm{E}}_{0}\mathrm{r}}{\left(\mathrm{r}+{\mathrm{r}}_{1}\right)}.\frac{l}{L}$

4. $\frac{{\mathrm{E}}_{0}\mathrm{l}}{\mathrm{L}}$

Two metal wires of indentical dimensions are connected in series. If ${\mathrm{\sigma}}_{1}$ and ${\mathrm{\sigma}}_{2}$ are the conductivities of the metal wires respectively, the effective conductivity of the combination is

1. $\frac{{\mathrm{\sigma}}_{1}{\mathrm{\sigma}}_{2}}{{\mathrm{\sigma}}_{1}+{\mathrm{\sigma}}_{2}}$

2. $\frac{2{\mathrm{\sigma}}_{1}{\mathrm{\sigma}}_{2}}{{\mathrm{\sigma}}_{1}+{\mathrm{\sigma}}_{2}}$

3. $\frac{{\mathrm{\sigma}}_{1+}{\mathrm{\sigma}}_{2}}{2{\mathrm{\sigma}}_{1}{\mathrm{\sigma}}_{2}}$

4. $\frac{{\mathrm{\sigma}}_{1+}{\mathrm{\sigma}}_{2}}{{\mathrm{\sigma}}_{1}{\mathrm{\sigma}}_{2}}$

A circuit contains an ammeter, a battery of 30 V and a resistance 40.8 ohm all connected in series. If the ammeter has a coil of resistance 480 ohm and a shunt of 20 ohm, the reading in the ammeter will be

(1) 1 A (2) 0.5 A

(3) 0.25 A (4) 2 A

A, B and C are voltmeters of resistance R, 1.5R and 3R respectively as shown in the figure. When some potential difference is applied between X and Y, the voltmeter readings are V_{A}, V_{B} and V_{C} respectively, then

(1) ${\mathrm{V}}_{\mathrm{A}}\ne {\mathrm{V}}_{\mathrm{B}}\ne {\mathrm{V}}_{\mathrm{C}}$

(2) ${\mathrm{V}}_{\mathrm{A}}={\mathrm{V}}_{\mathrm{B}}={\mathrm{V}}_{\mathrm{C}}$

(3) ${\mathrm{V}}_{\mathrm{A}}\ne {\mathrm{V}}_{\mathrm{B}}={\mathrm{V}}_{\mathrm{C}}$

(4) ${\mathrm{V}}_{\mathrm{A}}={\mathrm{V}}_{\mathrm{B}}\ne {\mathrm{V}}_{\mathrm{C}}$

A potentiometer wire has length 4 m and resistance 8 $\mathrm{\Omega}$. The resistance that must be connected in series with the wire and an accumulator of e.m.f. 2 V, so as to get a potential gradient 1 mV per cm on the wire is

(1) 48 $\mathrm{\Omega}$ (2) 32 $\mathrm{\Omega}$

(3) 40 $\mathrm{\Omega}$ (4) 44 $\mathrm{\Omega}$

When the key K is pressed at time t = 0, then which of the following statement about the current I in the resistor AB of resistance 1000 $\mathrm{\Omega}$ of the given circuit is true?

(1) I oscillates between 1 mA and 2 mA

(2) At t = 0, / = 2 mA and with time it goes to 1 mA

(3) I = 1 mA at all t

(4) I = 2 mA at all t

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 $\mathrm{\Omega}$. The power loss in the wire is

(1) 19.2 W (2) 19.2 kW

(3) 19.2 J (4) 12.2 kW

The resistances in the two arms of the meter bridge are 5 $\mathrm{\Omega}$ and R $\mathrm{\Omega}$, respectively. When the resistance R is shunted with an equal resistance, the new balance point is at 1.6 l_{1}. The resistance R, is

1. 10 $\mathrm{\Omega}$

2. 15 $\mathrm{\Omega}$

3. 20 $\mathrm{\Omega}$

4. 25 $\mathrm{\Omega}$

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 $\mathrm{\Omega}$, 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

(1) 0.25 $\mathrm{\Omega}$

(2) 0.95 $\mathrm{\Omega}$

(3) 0.5 $\mathrm{\Omega}$

(4) 0.75 $\mathrm{\Omega}$

In an ammeter 0.2% of main current passes through the galvanometer. If resistance of galvanometer is G, the resistance of ammeter will be

(1) $\frac{1}{499}\mathrm{G}$

(2) $\frac{499}{500}\mathrm{G}$

(3) $\frac{1}{500}\mathrm{G}$

(4) $\frac{500}{499}\mathrm{G}$

A wire of resistance 4 $\mathrm{\Omega}$ is stretched to twice its original length. The resistance of stretched wire would be

(1) 4 $\mathrm{\Omega}$

(2) 8 $\mathrm{\Omega}$

(3) 16 $\mathrm{\Omega}$

(4) 2 $\mathrm{\Omega}$

A : When a steady current flows through a conductor of non-uniform cross-section, the current density, electric field and drift velocity do not remain constant.

R : For a constant current the current density, electric field and drift velocity are inversely proportional to cross sectional area.

A : The voltage across a battery may be less, equal or more than the emf of the battery.

R : Voltage across a battery also depends on the magnitude and direction of current.

A : Practically a voltmeter will measure the voltage across the battery but not its EMF.

R : EMF of a cell is measured with the help of a potentiometer

A : A potentiometer can act as an ideal voltmeter.

R : An ideal voltmeter has infinite resistance.

A : When temperature of a metallic wire is increased, its resistance increases.

R : As the temperature is increased, average relaxation time increases.

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