NEET UG 2007 — Electromagnetism

A transformer is used to light a $100 \mathrm{~W}$ and $110 \mathrm{~V}$ lamp from a $220 \mathrm{~V}$ mains. If the main current is $0.5 \mathrm{amp}$, the efficiency of the transformer is approximately.

Nickel shows ferromagnetic property at room temperature. If the temperature is increased beyond Curie temperature, then it will show:

The resistance of an ammeter is $13 \Omega$ and its scale is graduated for a current upto 100 amps. After an additional shunt has been connected to this ammeter it becomes possible to measure currents upto 750 amperes by this meter. The value of shunt-resistance is:

Under the influence of a uniform magnetic field a charged particle is moving in a circle of radius $R$ with constant speed $v$. The time period of the motion:

The total power dissipated in watt in the circuit shown here is: 

A beam of clectron passes undeflected through mutually perpendicular electric and magnetic fields. If the electric field is switched off, and the same magnetic field is maintained, the electrons move:

What is the value of inductance $L$ for which the current is maximum in a series LCR circuit with $C=10 \mu \mathrm{F}$ and $\omega=1000$ $\mathrm{s}^{-1}$ ?

Three resistances $P, Q, R$ each of $2 \Omega$ and an unknown resistances $\mathrm{S}$ form the four arms of a Wheatstone bridge circuit. When a resistance of $6 \Omega$ is connected in parallel ot $\mathrm{S}$ the bridge gets balanced. What is the value of $\mathrm{S}$ ?

A hollow cylinder has a charge $q$ coulomb within it. If $\phi$ is the electric flux in units of voltmeter associated with the curved surface B, the flux linked with the plane surface $\mathrm{A}$ in units of voltmeter will be 

In a mass spectrometer for measuring the masses of ions, the ions are initially accelerated by an electric potential V and then made to describe semicircular paths of radius $R$ using a magnetic field $B$. If $V$ and $B$ are kept constant, the ratio $\left(\frac{\text { charge on the ion }}{\text { mass of the ion }}\right)$ will be proportional to:

Three point charges $+q,-2 q$ are placed at points $(x=0, y=a, z=0),(x=0, y=0, z$ $=0)$ and $(x=a, y=0, z=0)$ respectively. The magnitude and direction of the electric dipole moment vector of this charge assembly are:

Charges $+q$ and $-q$ are placed at points $\mathrm{A}$ and $\mathrm{B}$ respectively which are a distance $2 L$ apart, $\mathrm{C}$ is the midpoint between $\mathrm{A}$ and $\mathrm{B}$. The work done in moving a charge $+\mathrm{Q}$ along the semicircle CRD is 

Two condensers, one of capacity $C$ and other of capacity $C / 2$ are connected to a $V$-volt battery, as shown. The work done in charging fully both the condensers is 

A charged particle (charge $q$) is moving in a circle of radius $R$ with uniform speed $v$. The associated magnetic moment $\mu$ is given by:

The primary and secondary coils of a transformer have 50 and 1500 turns respectively. If the magnetic flux $\phi$ linked with the primary coil is given by $\phi=\phi_v+4 t$, where $\phi$ is in webers, $t$ is time in seconds and $\phi_v$ is a constant, the output voltage across the output voltage across the secondary coil is:

The electric and magnetic field of an electromagnetic wave are: