Current electricity practice · Medium

A set of $n$ identical resistors, each of resistance $R \Omega$, when connected in series have an effective resistance $X \Omega$ and when the resistors are connected in parallel, their effective resistance is $Y \Omega$. Find the relation between $R, X$ and $Y$.

A fuse wire with radius $\mathrm{1}\,\,\mathrm{mm}$ blows at $\mathrm{1}\mathrm{.5 }\,\mathrm{A}$. The radius of the fuse wire of the same material to blow at $\mathrm{3 }\,\mathrm{A}$ will be

Assertion: Two unequal resistances are connected in parallel across a cell, then current through the smaller resistance is more.
Reason: In a parallel combination the potential difference will be the same.

Every atom makes one free electron in copper. If $\mathrm{1}\mathrm{.1 }\,\mathrm{A}$ Current is flowing in the wire of copper having $\mathrm{1 mm}$ diameter, then the drift velocity(approx.) will be (density of copper = $9\,\, \times \,\,{10^3}\,\,\mathrm{k}\,\mathrm{g}{\mathrm{m}^{ - 3}}$ and atomic weight of copper =$\mathrm{63}$)

The thermo emf of copper-constantan couple is $40\,\mu V$ per degree. The smallest temperature difference that can be detected with this couple and a galvanometer of 100Ω resistance capable of measuring the maximum current of $1\,\,\mu A$ is

The resistance of an incandescent lamp is

The internal resistance of a dry cell is :

Two pieces of metallic wire having equal length and equal volume placed in air have different resistances. The two wires must :

Assertion (A) : If potential difference across two points is zero, current between these two points should be zero.

Reason (R): Current passing from a resistor $I=\frac{V}{R}$

A wire is cut into 4 pieces, which are put together by sides to obtain one conductor. If the original resistance of wire was $R$, the resistance of the buridle will be

A coil of wire of resistance $\mathrm{50}\,\,\mathrm{\Omega }$ is embedded in a block of ice and a potential difference of $\mathrm{210}\,\,\mathrm{V}$ is applied across it. The amount of ice which melts in $\mathrm{1}\,\,\mathrm{sec}$ is

A potentiometer wire is supplied a constant voltage of $3 \mathrm{~V}$. A cell of emf $1.08 \mathrm{~V}$ is balanced by the voltage drop across 216 con of the wire. Find the total length of the potentiometer wire.

Statement-1: When we connect a resistor to a battery, the flow of current starts almost instantaneously when switch is put on.
Statement-2: The random motion of electron takes place with a speed of the order of $10^6 \mathrm{~m} / \mathrm{s}$.

Kirchhoff's current law and voltage law respectively are based on the law of conservation of

The resistance of the filament of an electric bulb changes with temperature. If an electric bulb rated $\mathrm{220}\,\,\mathrm{volt}$ and $\mathrm{100}\,\,\mathrm{watt}$ is connected to $\left( {220\,\, \times \,\,.8} \right)\,\,volt$ sources, then the actual power would be

A copper wire of length 10 m and radius $({10^{ - 2}}/\sqrt \pi )\,\mathrm{m}$ has electrical resistance of $10\,\Omega$. The current density in the wire for an electric field strength of 10 (V/m) is:

When no electric field is present.

I. The electrons will be moving due to thermal motion during which they collide with the fixed ions.

II. An electron colliding with an ion emerges with the same speed as before the collision.

However the direction of its velocity after the collision is completely random.

III. At a given time, there is no preferential direction for the velocities of the electrons.

Thus, on an average, the number of electrons travelling in any direction will be equal to the number of electrons travelling in the opposite direction. So, there will be no net electric current.

Which of the above statements are correct?

Assertion: Kirchhoff's voltage law indicates that electrostatic field is conservative.
Reason: Potential difference between two points in a circuit does not depend on path.

The main power supply in India is at $220 {~V}$, whereas that in the US is at $110 {~V}$. Which one among the following statements in this regard is correct?

When a long straight uniform rod is connected across an ideal cell, the drift velocity of electrons in it is ${v}$. If a uniform hole is made along the axis of the rod and the same battery is used, then the drift velocity of electrons becomes

A thermister is dipped in a bath whose temperature is to be measured. When the temperature increase the current also increase, because of decreases in

A current $I$ is passed for a time $t$ through a number of voltmeters. If $m$ is the mass of a substance deposited on an electrode and $z$ is its electrochemical equivalent, then

An electric water kettle rated $\mathrm{2}\mathrm{.1 }\,\mathrm{kW}$ is filled with $\mathrm{1}\mathrm{.5 }\,\,\mathrm{kg}$ of water at $20\,{\,^0}\mathrm{C}$. How many seconds does it take to reach the boiling point of water? Assume that there are no heat losses from the kettle. Specific heat capacity of water is $4200\,\,\mathrm{Jk}{\mathrm{g}^{ - 1}}\,{\mathrm{K}^{ - 1}}$

Charge through a cross-section of a conductor is given by $Q=\left(t^5+2 t\right)$ coulomb. The instantaneous current through the conductor at $t=1 \mathrm{~s}$ is

When an electrical appliance is switched on, it responds almost immediately, because

Kirchhoff's first law is based on the law of conservation of

By what percentage will the illumination of the lamp decrease if the current drops by $20 \%$ ?

The resistance of a straight conductor does not depend on its

Heat produced (cals) in a resistance $R$ when a current $I$ amperes flows through it for $t$ seconds is given by the expression

To get maximum current through a resistance of $2.5\, \Omega$, one can use $m$ rows of cells, each row having $n$ cells. The internal resistance of each cell is $0.5 \, \Omega$. The values of $n$ and $m$, if the total number of cells is 45, are