$A$ steel tape gives correct measurement at $20^{\circ} C$. $A$ piece of wood is being measured with the steel tape at $0^{\circ} C$. The reading is $25 \ cm$ on the tape. The real length of the given piece of wood must be:

Explain linear expansion. Write its unit.

Two metal strips that constitute a thermostat must necessarily differ in their

$A$ uniform rod of length $L$ pivoted at one end $P$ is freely rotated in a horizontal plane with an angular velocity $\omega$ about a vertical axis passing through $P$. If the temperature of the system is increased by $\Delta T$, the angular velocity becomes $\frac{\omega}{2}$. If the coefficient of linear expansion of the rod is $\alpha$ (where $\alpha \ll 1$), then $\Delta T$ will be:

$A$ metal tape is calibrated at $25^{\circ} C$. On a cold day when the temperature is $-15^{\circ} C$,the percentage error in the measurement of length is (Coefficient of linear expansion of metal $= 1 \times 10^{-5} {}^{\circ} C^{-1}$) (in $\%$)

To keep constant time,watches are fitted with a balance wheel made of: