Current electricity practice · Mixed difficulty

In which of the following cases ohm's law is not valid?

In the above question if potential difference is applied, the drift velocity at temperature $T$ is

Show that one ampere is equivalent to a flow of $6.25 \times 10^{18}$ elementary charges per second.

Wires ${P}$ and ${Q}$ are having same resistance at room temperature. When heated, resistance of ' $P$ ' increases, and that of ' $Q$ ' decreases, we conclude that

Which of the following statements are incorrect?

I. The order of magnitude of current flowing in household appliances is one ampere.

II. The order of magnitude of current in lightening is about one ampere.

III. The order of magnitude of current in nerves in human body is one ampere.

When the temperature of a metallic resistor is increased, the product of its resistivity and conductivity

The current density of a solid cylindrical wire of radius ${R}$, as a function of radial distance ${r}$ is given by $J(r)=J_0\left(1-\frac{r}{R}\right)$. The total current in the radial region ${r}=0$ to $r=\frac{R}{4}$ will be:

Assertion: Potentiometer measures the correct value of emf of a cell.
Reason: No current flows through the cell being balanced at the null point of potentiometer.

A potential difference $V$ is applied to a copper wire. If the potential difference is increased to $2 V$, then the drift velocity of electrons will:

Equal amounts of a metal are converted into cylindrical wire of different lengths $L$ and cross-sectional area $A$.The wire with the maximum resistance is the one, which has

If a current is allowed to pass through a circuit consisting of two dissimilar metals, there is either evolution or absorption of heat at the junction, depending upon the direction of the current. The effect is known as

Statement-I: Potential difference across the terminals of a battery is always less than emf of the battery.
Statement-II: During discharging of a battery potential difference across the terminals of a battery is less than its emf.

The unit of electrical conductivity is

Two potentiometers A and B having 4 wires and 10 wires, each having $100 \mathrm{~cm}$ in length are used to compare e.m.f. of 2 cells. Which one will give a larger balancing length?

Assertion: A larger dry cell has higher emf.

Reason: The emf of a dry cell is proportional to its size.

If for a thermocouple ${T_n}$ is the neutral temperature, ${T_c}$ is the temperature of the cold junction and ${T_i}$ is the temperature of inversion, then

Two wires $A$ and $B$ made of same material and having their lengths in the ratio $6: 1$ are connected in series. The potential difference across the wires are $3 \mathrm{~V}$ and $2 \mathrm{~V}$ respectively. If $r_A$ and $r_B$ are the radii of $A$ and $B$ respectively, then $\frac{r_B}{r_A}$ is

In a thermocouple, which of the following statements is not true

In household electric circuit

I. all electric appliances drawing power are joined in parallel

II. a switch may be either in series or in parallel with the appliance which it controls III. if a switch is in parallel with an appliance, it will draw power when the switch is in the 'off' position (open)

IV. if a switch is in parallel with an appliance, the fuse will blow (burn out) when the switch is put 'on' closed.

Which of the above statements are correct?

A constant voltage is applied between two ends of a metallic wire. If the wire is replaced by another wire of same material, half the length and doubled the radius, the rate of heat developed in the wire will be:

To draw maximum current from a combination of cells, how should the cells be grouped?

As the temperature rises the resistance offered by metal

In water voltmeter, the electrolysis of …… takes place

Two discharge tubes have identical material structure and the same gas is filled in them. The length of one tube is $10 \mathrm{~cm}$ and that of the other tube is $20 \mathrm{~cm}$. Sparking starts in both the tubes when the potential difference between the cathode and the anode is $100 \mathrm{~V}$. If the pressure in the shorter tube is $1.0 \mathrm{~mm}$ of mercury, what is the pressure in the longer tube?

Faraday’s ${\mathrm{2}^{\mathrm{nd}}}$ law states that mass deposited on the electrode is directly proportional to

For driving a current of 3 Afor 5 minutes in an electric circuit, $900 \mathrm{~J}$ of work is to be done. Find the emf of the source in the circuit.

Assertion: A voltmeter must be connected in parallel in a circuit and it should have a high resistance.
Reason: The voltmeter in the circuit must not affect the potential difference measured by it.

The ratio of resistance of two copper wires of the same length and of same cross-sectional area when connected in series to that when connected in parallel is

Two wires of same material have length $L$ and $2\,L$ and cross-sectional areas $4\,\,A$ and $A$ respectively. The ratio of their specific resistances would be

For a metallic wire, the ratio $\frac{V}{i}(V =$ applied potential difference and $i$ =current flowing ) is