Why is the total resistance of a voltmeter kept very high?

$A$ voltmeter essentially consists of

$A$ voltmeter of resistance $1000\,\Omega$ gives full scale deflection when a current of $100\,mA$ flows through it. The shunt resistance required across it to enable it to be used as an ammeter reading $1\,A$ at full scale deflection is ............... $\Omega$.

The circular coil of a galvanometer has $50$ turns. The coil has a radius of $1 \ cm$. The coil is placed in a radial magnetic field of $0.010 \ T$. The torsion coefficient of the spring on which the coil hangs is $3 \times 10^{-7} \ N-m-rad^{-1}$. Determine the deflection of the galvanometer's pointer if the current through the coil is $1.0 \ mA$. (in $^{\circ}$)

The scale of a galvanometer is divided into $25$ equal divisions. The resistance of the galvanometer is $100 \,\Omega$. The current sensitivity of the galvanometer is $4 \times 10^{-4} \,A/div$. What resistance in $ohm$ must be connected in series to measure $2.5 \,V$?

$A$ galvanometer of resistance $10 \Omega$ changes its range from $1 \text{ mA}$ to $101 \text{ mA}$ when a resistive wire is connected in parallel. If the resistivity of the material of the wire and its area of cross-section are $1 \times 10^{-6} \Omega \text{ m}$ and $1 \text{ mm}^2$ respectively,then the length of the wire is (in $cm$)