A torch bulb rated as $4.5\, W, 1.5\, V$ is connected as shown in the figure. The $e.m.f.$ of the cell needed to make the bulb glow at full intensity is ............. $V$
Medium
Download our app for free and get started
Resistance of bulb is
$\frac{1.5 \times 1.5}{4.5} \Omega=0.5 \Omega$
Resistance of parallel combination,
$R=\frac{1 \times \frac{1}{2}}{1+\frac{1}{2}} \Omega=\frac{1}{3} \Omega$
Now, $r=\frac{E-V}{V} R$ or $\frac{8}{3}=\frac{E-1.5}{1.5} \times \frac{1}{3}$ or $E=13.5 \mathrm{V}$
Download our appand get started for free
Experience the future of education. Simply download our apps or reach out to us for more information. Let's shape the future of learning together!No signup needed.*
Similar Questions
- 1Inside $a$ super conducting ring six identical resistors each of resistance $R$ are connected as shown in figure. Imagine a battery of $emf$ $E$ between the point $0$ and $1$, with its positive terminal connected with $O.$View Solution
- 2The resistance of platinum wire at $0^{\circ}\,C$ is $2\,\Omega$ and $6.8\,\Omega$ at $80^{\circ} \,C$. The temperature coefficient of resistance of the wire is :View Solution
- 3Net resistance between $X$ and $Y$ is ............... $\Omega$View Solution
- 4A potential difference of $V$ is applied at the ends of a copper wire of length $l$ and diameter $d$. On doubling only $d$, drift velocityView Solution
- 5Voltmeter reads potential difference across the terminals of an old battery as $1.2\,volt$ , while a potentiometer reads $1.4\,volt$ . The internal resistance of battery is $40\,\Omega $ , then voltmeter resistance is .............. $\Omega$View Solution
- 6The storage battery of a car has an $emf$ of $12\; V$. If the internal resistance of the battery is $0.4\; \Omega,$ what is the maximum current (in $A$) that can be drawn from the battery?View Solution
- 7The circuit shown here has two batteries of $8.0\,V$ and $16.0\,V$ and three resistors $3\,\Omega ,\,9\,\Omega $ and $9\,\Omega $ and a capacitor of $5.0\,\mu F.$View Solution
How much is the current $I$ in the circuit in steady state? ................... $A$
- 8A potentiometer having the potential gradient of $2\, mV/cm$ is used to measure the difference of potential across a resistance of $10 \,\Omega$. If a length of $50\, cm$ of the potentiometer wire is required to get the null point, the current passing through the $10 \,\Omega$ resistor is (in $mA$)View Solution
- 9In an electric heater $4\, amp$ current passes for $1$ minute at potential difference of $250\, volt$, the power of heater and energy consumed will be respectivelyView Solution
- 10Resistance of a carbon resistor determined from colour codes is $(22000 \pm 5 \%) \Omega$. The colour of third band must be :View Solution