Surface tension by capillary rise — practice questions

Question 1 · difficulty L1 · recall

Capillary rise in a narrow tube is caused by

• A. surface tension together with wetting forces and pressure difference
• B. gravity alone pulling liquid upward
• C. magnetic attraction only
• D. radioactive forces

Question 2 · difficulty L1 · understanding

For a liquid that wets the capillary with contact angle θ, the rise h is approximately

• A. h=Tρgr
• B. h=2T cosθ/(ρgr)
• C. h=ρgr/(2T)
• D. h=2Tr/(ρg)

Question 3 · difficulty L2 · understanding

Capillary rise is larger in a tube with

• A. larger radius
• B. the same radius but no surface tension
• C. smaller radius
• D. zero contact with liquid

Question 4 · difficulty L2 · application

For a wetting liquid with θ≈0, cosθ is approximately

• A. 0
• B. -1
• C. 1/2 necessarily
• D. 1

Question 5 · difficulty L3 · application

If capillary radius is doubled while other quantities stay fixed, rise becomes

• A. one-half
• B. twice
• C. four times
• D. unchanged

Question 6 · difficulty L3 · application

If liquid density increases at fixed T, r and θ, capillary rise

• A. increases
• B. decreases
• C. stays fixed
• D. changes sign automatically

Question 7 · difficulty L4 · analysis

A liquid depresses rather than rises in a capillary when

• A. cosθ is positive
• B. surface tension is zero only
• C. cosθ is negative
• D. density is zero

Question 8 · difficulty L4 · analysis

Why should the capillary tube be clean in this experiment?

• A. Cleaning changes gravitational acceleration
• B. Dirt is required to define radius
• C. Surface tension is independent of surface condition
• D. Contamination can alter contact angle and surface tension

Question 9 · difficulty L5 · analysis

A liquid of T=0.072 N/m, ρ=1000 kg/m³ rises in a tube of r=0.5 mm with θ≈0 and g≈9.8 m/s². h is closest to

• A. 2.9 cm
• B. 0.29 cm
• C. 29 cm
• D. 1.4 mm

Question 10 · difficulty L5 · analysis

If a student's measured tube radius is 5% too large, the surface tension calculated from T=hρgr/(2cosθ) will, other readings fixed, be

• A. about 5% too small
• B. about 5% too large
• C. about 10% too small
• D. unchanged