If a resistance coil is made by joining in parallel two resistances each of 20$\Omega$. An emf of 2V is applied across this coil for 100 seconds. The heat produced in the coil is

(1) 20 J

(2) 10 J

(3) 40 J

(4) 80 J

Which of the following graphs correctly represents the variation of mobility $\left(\mathrm{\mu }\right)$ of electrons with applied electric field (E) in a metallic conductor?

1.  

2.  

3.  

4.  

If I be the current limit of a fuse wire of length l and radius r, then select the appropriate relation

(1) $I \alpha l$

(2) $I \alpha r^2$

(3) $I \alpha l^0$

(4) $I \alpha r^0$

The resistance of platinum wire at 0$°\mathrm{C}$ is 22.05 $\mathrm{\Omega }$ and at 100$°\mathrm{C}$ it becomes 22.70 $\mathrm{\Omega }$. When the wire is heated to a temperature of t$°\mathrm{C}$ the resistance of wire becomes 24.91$\mathrm{\Omega }$. The value of t is 

1.  220

2.  440

3.  310

4.  550

The sensitivity of a potentiometer can be increased by

1.  increasing the potential gradient

2.  decreasing the length of potentiometer wire

3.  decreasing the current in the potentiometer wire

4.  all of these

$\mathrm{In} \mathrm{the} \mathrm{circuit} \mathrm{shown} \mathrm{in} \mathrm{figure} \mathrm{if} \mathrm{power} \mathrm{dissipated} \mathrm{in} 9\mathrm{\Omega } \mathrm{resistor} \mathrm{is} 144\mathrm{W}, \mathrm{then} \mathrm{potential} \mathrm{difference} \mathrm{across} 3.6\mathrm{\Omega } \mathrm{resistor} \mathrm{will} \mathrm{be}$

1.  36V

2.  18V

3.  9V

4.  Zero

A current of 1 mA is flowing through a copper wire. How many electrons will pass a given point in one second  $\left[\mathrm{e} = 1.6 \times {10}^{-19} \mathrm{Coulomb}\right]$

1.  $6.25 \times {10}^{19}$

2.  $6.25 \times {10}^{15}$

3.  $6.25 \times {10}^{31}$

4.  $6.25 \times {10}^8$

The drift velocity of free electrons in a conductor is 'v' when a current 'i' is flowing in it. If both the radius and current are doubled, then drift velocity will be :

1.  v

2.  $\frac{\mathrm{v}}{2}$

3.  $\frac{\mathrm{v}}{4}$

4.  $\frac{\mathrm{v}}{8}$

A battery has e.m.f. 4V and internal resistance r. When this battery is connected to an external resistance of 2 ohms, a current of 1 amp. flows in the circuit. How much current will flow if the terminals of the battery are connected directly

1.  1 Amp

2.  2 Amp

3.  4 Amp

4.  Infinite

Current I as shown in the circuit will be

1.  10 A

2.  $\frac{20}{3} \mathrm{A}$

3.  $\frac{2}{3} \mathrm{A}$

4.  $\frac{5}{3} \mathrm{A}$