It is expressed by scientific counting method: 0.0045m =? Um =? Nm, 1m =? Mm =? Um =? Nm It is expressed by scientific counting method: 1m =? Mm =? Um =? Nm 0.0045m=?um＝?nm, 1500000cm＝?km 78um＝?m

It is expressed by scientific counting method: 0.0045m =? Um =? Nm, 1m =? Mm =? Um =? Nm It is expressed by scientific counting method: 1m =? Mm =? Um =? Nm 0.0045m=?um＝?nm, 1500000cm＝?km 78um＝?m

The following "^" represents several powers. 10 ^ 3 is the third power of 10
1m=1×10^3mm=1×10^6um=1×10^9nm
0.0045m=4.5×10^3um=4.5×10^6nm
1500000cm=15km
78um=7.8×10^-5m

0.0045m =? Um =? Nm, 0.25m =? Um =? Nm, please use scientific counting method,

0.0045m=4.5×10^3um=4.5×10^6nm,0.25m=2.5*10^5um=2.5*10^8nm

Complete the following unit conversion, learn to use scientific notation to express the physical results: (1) 8cm=______ µm　（2）4.2nm=______ cm   （3）6.7dm=______ km （4）0.18km=______ m（5）1.7dm=______ cm=______ mm______ nm______ µm  （6）20min=______ h      （7）0.5h=______ min=______ s．

(1) 8cm = 8 × 104 μ m; (2) 4.2cm = 4.2 × 10-7cm; (3) 6.7dm = 6.7 × 10-4cm; (4) 0.18km = 0.18 × 103m = 180m; (5) 1.7dm = 17cm = 170mm = 170 × 106nm = 1.7 × 108nm = 1.7 × 105 μ m; (6) 20min = 20 ／ 60H = 0.33h; (7) 0.5h = 0.5 × 60min = 30min = 30 × 60s = 1800s; therefore, the answers are: (1) 8 × 104; (2) 4.2 × 10-7; (3) 6.7 × 10-4; (4) 180; (5) 17; 170; 1.5 7×108；1.7×105；（6）0.33；（7）30；1800；