Right-hand thumb rule is used :
This rule is used to determine the direction of the magnetic field. If we rotate aright-handed screw using a screwdriver, then the direction of current is the same as the direction in which the screw advances and the direction of rotation of the screw gives the direction of the magnetic field.

The required resistance has the least value for ammeter and maximum value in the case of a voltmeter.
(i) The shunt resistance required to convert a galvanometer to an ammeter has the value
S = \(\frac { { I }_{ g } }{ I-{ I }_{ g } } \) x G
The shunt required for the milliammeter be a higher value.
(ii) Similarly, The voltmeter should have high resistance, the value of the required resistance should be highest in the case of the voltmeter. This is connected in series with the coil of the galvanometer.

A galvanometer cannot be used for measuring the current
(i) A galvanometer has a finite large resistance and is connected in series in the circuit. So it will increase the resistance of circuit and hence change the value of current in the circuit.
(ii) A galvanometer is a very sensitive device, it gives a full scale deflection for the current of the order of microampere hence if connected, it will not measure current of the order of ampere.

Magnetic field due to current carrying wire is perpendicular to plane of paper - downward

i.e \(\vec { B } =-\frac { { \mu }_{ 0 }I }{ 2\pi f } \hat { v } \)
Force \(\vec { F } =q(\vec { v } \times \vec { B } )=e\left[ (-v\hat { j } )\times \left( \frac { { \mu }_{ 0 }I }{ 2\pi f } \hat { v } \right) \right] \)
= \(\frac { { \mu }_{ 0 }evI }{ 2\pi d } \hat { i } \)
That is the magnetic force has magnitude \(\frac { { \mu }_{ 0 }evI }{ 2\pi d } \) and is directed along +ve X-axis i.e in the plane of paper perpendicular to the direction of \(\vec { v } \) and to the right.

w = \(\frac { qB }{ m } \) independence of angle of the entrance with the magnetic field.
W₁ : w₂ = 1 : 1